Directional backlight

ABSTRACT

Disclosed is a light guiding valve apparatus including at least one transparent stepped waveguide optical valve for providing large area collimated illumination from localized light sources, and at least one further illumination source. A stepped waveguide may be a stepped structure, where the steps include extraction features hidden to guided light, propagating in a first forward direction. Returning light propagating in a second backward direction may be refracted, diffracted, or reflected by the features to provide discrete illumination beams exiting from the top surface of the waveguide. Such controlled illumination may provide for efficient, multi-user autostereoscopic displays as well as improved 2D display functionality. Light from a separate illumination source may pass through the transparent stepped waveguide optical valve to provide at least one further additional illumination function.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority to U.S. Provisional Patent ApplicationNo. 61/648,840, entitled “Stepped imaging directional backlight arrays,”filed May 18, 2012; U.S. Provisional Patent Application No. 61/648,942,entitled “Cross talk suppression apparatus and method thereof,” filedMay 18, 2012; to U.S. Provisional Patent Application No. 61/649,050,entitled “Control system for a directional light source,” filed May 18,2012; to U.S. Provisional Patent Application No. 61/649,054, entitled“Wide angle imaging directional backlights,” filed May 18, 2012; to U.S.Provisional Patent Application No. 61/649,116, entitled “Polarizationrecovery in imaging directional backlights,” filed May 18, 2012; to U.S.Provisional Patent Application No. 61/649,136, entitled “Diffractivereflectors for imaging directional backlights,” filed May 18, 2012, allof which are herein incorporated by reference in their entirety.

TECHNICAL FIELD

This disclosure generally relates to illumination of light modulationdevices, and more specifically relates to light guides for providinglarge area illumination from localized light sources for use in 2D, 3D,and/or autostereoscopic display devices.

BACKGROUND

Spatially multiplexed autostereoscopic displays typically align aparallax component such as a lenticular screen or parallax barrier withan array of images arranged as at least first and second sets of pixelson a spatial light modulator, for example an LCD. The parallax componentdirects light from each of the sets of pixels into different respectivedirections to provide first and second viewing windows in front of thedisplay. An observer with an eye placed in the first viewing window cansee a first image with light from the first set of pixels; and with aneye placed in the second viewing window can see a second image, withlight from the second set of pixels.

Such displays have reduced spatial resolution compared to the nativeresolution of the spatial light modulator and further, the structure ofthe viewing windows is determined by the pixel aperture shape andparallax component imaging function. Gaps between the pixels, forexample for electrodes, typically produce non-uniform viewing windows.Undesirably such displays exhibit image flicker as an observer moveslaterally with respect to the display and so limit the viewing freedomof the display. Such flicker can be reduced by defocusing the opticalelements; however such defocusing results in increased levels of imagecross talk and increases visual strain for an observer. Such flicker canbe reduced by adjusting the shape of the pixel aperture, however suchchanges can reduce display brightness and can include addressingelectronics in the spatial light modulator.

BRIEF SUMMARY

According to a first aspect of the present disclosure, there is provideda directional display device, which may include a transmissive spatiallight modulator. The transmissive spatial light modulator may include anarray of pixels arranged to modulate light passing therethrough and atleast two directional backlights. Each of the at least two directionalbacklights may include a waveguide having an input end, first andsecond, opposed guide surfaces for guiding light along the waveguide,and a reflective end facing the input end for reflecting light from theinput light back through the waveguide. The first guide surface may bearranged to guide light by total internal reflection, the second guidesurface may have a plurality of light extraction features oriented toreflect light guided through the waveguide after reflection from thereflective end in directions allowing exit through the first guidesurface as output light. The waveguide may be arranged to direct inputlight originating from different input positions in a lateral directionacross the input end into respective optical windows in outputdirections distributed in the lateral direction in dependence on theinput positions, the directional backlights each being arranged tosupply output light through the spatial light modulator.

The directional backlights may be stacked and/or tiled behind thespatial light modulator, that is the spatial light modulator is arrangedbetween the directional backlight and a window plane. In this case, thedirectional backlights may supply output light through different regionsof the spatial light modulator.

The present embodiments may achieve a combination of optical windowproperties that may include but are not limited to increased brightness,increased window resolution, landscape and portrait operation, increasedviewing freedom, mixing of different color directional illumination,increased longitudinal viewing freedom and increased display size.

Tiled arrangements may advantageously achieve increased display sizewhile maintaining a desirable image luminance for given light emittingelement luminous emittance. Further, longitudinal viewing freedom may beextended in cooperation with observer tracking display control systems.Further cross talk may be reduced in scanning display systems. Furtheroptical aberrations of viewing windows may be reduced, increasinglateral viewing freedom while maintaining a desirable level of imagecross talk. Further the size of display bezel may be reduced.

In one embodiment, first and second directional backlights of thedirectional backlights may be tiled in a direction perpendicular to thelateral direction. Stated differently, the directional backlights may betiled in the direction of the optical axes of the waveguides. Further,the first directional backlight may have a reflective end, and thereflective end of the first directional backlight may overlap the seconddirectional backlight. Additionally, a third directional backlight mayalso be tiled in the lateral direction.

In another embodiment, the directional backlights may be tiled in thelateral direction. Stated differently, the directional backlights may betiled in a direction perpendicular to the optical axes of thewaveguides.

In some embodiments, the directional backlights may be formed from acommon piece of material.

Advantageously embodiments including directional backlights that aretiled in the lateral direction may achieve extended longitudinal viewingfreedom. The individual directional backlights may have a width that issmaller than the width of the spatial light modulator that achieves anincreased range of longitudinal viewing freedom for the respectivedirectional backlight from geometrical considerations. The individualdirectional backlights may cooperate with an observer tracking systemsso that each directional backlight may be arranged to direct light to anobserver that achieves the longitudinal viewing freedom of the displayapparatus that is substantially the same as the longitudinal viewingfreedom of the individual directional backlights.

The directional backlights may be stacked behind the spatial lightmodulator. In this case, the directional backlights may each supplyoutput light through the spatial light modulator and through any otherdirectional backlight intermediate the directional backlight and thespatial light modulator. The directional backlights may be orientedaround the approximate normal to the spatial light modulator so that theoptical windows of the directional backlights may be approximatelyaligned with each other. The optical windows of the directionalbacklights may extend at an angle relative to each other in anapproximate range from 85 to 95 degrees. Additionally, the first guidesurfaces of the respective directional backlights may be substantiallycoplanar. Further, the first guide surfaces may be substantiallycoplanar whether or not the directional backlights are oriented aroundthe approximate normal to the spatial light modulator.

Continuing the discussion of this case, the directional backlights maybe arranged in inverted orientations around the approximate normal tothe spatial light modulator with the input end of each directionalbacklight on the same side as the reflective end of the otherdirectional backlight. The optical windows of the directional backlightsmay or may not be approximately aligned with each other. The first guidesurfaces of the respective directional backlights may or may not besubstantially coplanar. Also, the guide surfaces of the facing guidesurfaces of the two directional backlights may be arranged in invertedorientations which may extend in a generally parallel direction.

The directional backlight may include a reflective end which may havepositive optical power in a lateral direction across the waveguide andmay also include an input end that is an extension of one of the guidesurfaces, and a coupler facing the input end which may be arranged todeflect input light along the waveguide.

Each of the directional backlights may include light extraction featureswhich may be facets of the second guide surface. The second guidesurface may have regions alternating with the facets which may bearranged to direct light through the waveguide without extracting it. Inone example, the light extraction features of each directional backlightmay have positive optical power in a lateral direction across thewaveguide.

A directional display device may also include in respect of eachdirectional backlight, an array of light sources at different inputpositions across the input end of the respective waveguide. In oneexample of the directional display device, the directional backlightsmay be oriented around the approximate normal to the spatial lightmodulator so that the optical windows of the directional backlights maybe approximately aligned with each other and the array of light sourcesin respect of each directional backlight may be arranged to output lightof a different color.

A directional display apparatus including this display device may alsoinclude a control system which may be arranged to selectively operatethe light sources to direct light into viewing windows corresponding tooutput directions. Further, this directional display apparatus may be anautostereoscopic display apparatus in which the control system may befurther arranged to control the display device to display temporallymultiplexed light and right images and also to display substantiallysynchronously to direct the displayed images into viewing windows inpositions approximately corresponding to left and right eyes of anobserver. The control system may also be arranged to direct thedisplayed images into viewing windows in positions approximatelycorresponding to left and right eyes of an observer, which may primarilydepend on the detected position of the observer. The control system ofthis display apparatus may include a sensor system which may be arrangedto detect the position of an observer relative to the display device.The sensor system may be arranged to detect the position of an observerrelative to the display device laterally and longitudinally to thenormal to the spatial light modulator. The control system may bearranged to direct the displayed images into viewing windows inpositions corresponding to left and right eyes of an observer, which mayprimarily depend on the detected position of the observer.

The above descriptions may apply to each or all of the followingapparatuses, modifications and/or additional features, individually, orany combination thereof, which will now be described.

Advantageously the directional backlights of the present embodiments maybe arranged in stacked arrangements. Such directional backlights may bearranged to be substantially transparent to incident light from anexternal light source and so may substantially have no effect on lightfrom other directional backlights and may be independently controlled,achieving the advantageous combination of window arrangements includingincreased window resolution, increased window brightness, multiplewindow orientations and other advantageous window arrangements describedherein.

Known wedge waveguides such as described in [Travis] may achieve lightextraction by means of breaking total internal reflection between twoplanar guiding sides and require a light deflection element to deflectlight towards a direction around a normal direction of the surface ofthe spatial light modulator. The present embodiments do not require alight deflection element and do not substantially direct light close toparallel to a planar guiding surface. If such wedge waveguides were tobe stacked in a first arrangement, each including a light deflectionelement, the second light deflection element would further deflect lightfrom the first waveguide, so that the angular outputs could not beindependently controlled. If such wedge waveguides were stacked in asecond arrangement with a single shared output light deflection element,then light from the first wedge waveguide incident on the second wedgewaveguide would show high light loss due to Fresnel reflections forlight incident near parallel to the surface. Advantageously the presentembodiments do not have the undesirable properties of stacked wedgewaveguides.

According to a further aspect of the present disclosure, there may beprovided a directional illumination apparatus may include a first lightextraction element for guiding and extracting light. The first lightextraction element may include a first light guiding surface and asecond light guiding surface, opposite the first light guiding surface,and a first illumination input surface located between the first andsecond light guiding surfaces. The first illumination input surface maybe operable to receive light from a first array of light sources and asecond light extraction element for guiding and extracting light. Thesecond light extraction element may include a third light guidingsurface, and a fourth light guiding surface opposite the third lightguiding surface. Additionally, the second light extraction element mayinclude a second illumination input surface located between the thirdand fourth light guiding surfaces, and the second illumination inputsurface may be operable to receive light from a second array of lightsources. The light from the second light extraction light element may bedirected at least in part through a surface of the first lightextraction element other than the first illumination input.

According to a further aspect of the present disclosure, there may beprovided a directional illumination system, which may include a firstlight extraction element for guiding and extracting light. The firstlight extraction element may include a first section operable to allowlight rays to spread and a second section. The second section mayinclude a first light guiding surface, and a second light guidingsurface opposite the first light guiding surface, and a firstillumination input surface located between the first and second lightguiding surfaces. The first illumination input surface may be operableto receive light from a first array of light sources and from a secondlight extraction element for guiding and extracting light. The secondlight extraction element may include a third section operable to allowlight rays to spread and a fourth section which may further include athird light guiding surface, a fourth light guiding surface opposite thethird light guiding surface, and a second illumination input surfacelocated between the third and fourth light guiding surfaces. The secondillumination input surface may be operable to receive light from asecond array of light sources, in which light from the second lightextraction light element may be directed at least in part through asurface of the first light extraction element other than the firstillumination input surface.

According to a further aspect of the present disclosure, there may beprovided a directional illumination apparatus which may include at leasttwo optical valves for guiding light, in which each optical valvefurther may include a first light guiding surface. The first lightguiding surface may be substantially planar and a second light guidingsurface, opposite the first light guiding surface, may include aplurality of guiding features and a plurality of extraction features, inwhich the plurality of extraction features may be operable to allowlight to pass with substantially low loss when the light is propagatingin a first direction. The optical valves in cooperation with respectiveapproximately aligned light sources may be arranged to provide differentdirectional illuminations.

According to a further aspect of the present disclosure, there may beprovided a light guiding system that provides directional distributions,which may include a directional illumination apparatus. The directionalillumination apparatus may include at least two optical valves forguiding light, in which each optical valve may further include a firstlight guiding surface that may be substantially planar, and a secondlight guiding surface, opposite the first light guiding surface. Thesecond light guiding surface may include at least one guiding featureand a plurality of extraction features, in which the plurality ofextraction features may be operable to allow light to pass withsubstantially low loss when the light is propagating in a firstdirection and further operable to reflect light to exit the opticalvalve when the light is propagating in a second direction. A spatiallight modulator may be operable to receive light from at least one ofthe two optical valves in which the optical valves in cooperation withrespective approximately aligned light sources may be arranged toprovide different directional illuminations.

Devices and apparatuses in accordance with the present disclosure mayemploy any of the following features.

Display backlights in general employ waveguides and edge emittingsources. Certain imaging directional backlights have the additionalcapability of directing the illumination through a display panel intoviewing windows. An imaging system may be formed between multiplesources and the respective window images. One example of an imagingdirectional backlight is an optical valve that may employ a foldedoptical system and hence may also be an example of a folded imagingdirectional backlight. Light may propagate substantially without loss inone direction through the optical valve while counter-propagating lightmay be extracted by reflection off tilted facets as described in patentapplication Ser. No. 13/300,293, which is herein incorporated byreference, in its entirety.

Backlight units (BLUs) that employ folded optical systems such asstepped imaging directional backlights may be advantageously transparentto normally incident light. The transparency property enables valvearray apparatuses such as stacked and tiled composite illuminationsystems of the present embodiments, where for example at least part ofadjacent illuminators are hidden by or illuminate through each other.Such valve array illumination apparatus embodiments lead to increasedbrightness, local independent illumination and directional capabilities.

Combining backlights, for example by means of stacking or tilingbacklight illumination units increases brightness and provides for localspatial and directional independence of respective backlights. In timemultiplexed LCD systems, local illumination increases visible contrastand minimizes frame to frame contamination in stereoscopic systemsproviding scrolling illumination schemes. In the specific case of theoptical valve, the ability to tile illuminators in a mosaic by means ofstacking and/or tiling alleviates many of the optical issues present inlarge area illumination. Stacking and tiling also enables mixedillumination systems where a transparent directional backlight can beilluminated by a more conventional 2D illumination apparatus.

Additionally, embodiments may relate to a directional backlightapparatus and a directional display device which may incorporate thedirectional backlight. Such an apparatus may be used forautostereoscopic displays, privacy displays, multi-user displays andother directional display applications.

In embodiments, the optical function of the directional backlights canbe provided by multiple stepped waveguides in which light passes from anexternal light source passes through a surface of the stepped waveguidein addition to the input aperture of the stepped waveguide.Advantageously such an arrangement provides additional optical functionsto be provided in addition to the optical function provided by therespective stepped waveguide while preserving the advantages of highefficiency, large back working distance and thin form factor of therespective stepped waveguide.

Advantageously such an arrangement achieves a combination of opticalfunctions including, but not limited to, increased brightnessautostereoscopic display, a controllable landscape/portrait display, a2D/3D switchable display, increased display area, and high efficiencycolor display illumination. Further the optical properties of the outputcan be modified to increase uniformity and widen viewing angle. Further,multiple viewers can be tracked independently.

The stepped waveguide does not require substantial redirection of theoutput illumination beam using serrated polymer films and asymmetricdiffusers and as such, the optical valve discussed herein may betransparent to near normal incident light, or may not substantiallychange the directionality of light passing through the light guidingsurfaces of the stepped waveguide. Advantageously, such an arrangementenables a stacking of stepped imaging directional backlights to beprovided wherein the operation of the stepped imaging directionalbacklights may be substantially independent, thus achieving multiplefunctionalities. Further, arrays of stepped waveguides can be arrangedas tiles in which light from adjacent stepped waveguide tiles may bedirected within guiding layers to provide an increased cone angle.

Embodiments herein may provide an autostereoscopic directional displaydevice with large area and thin structure. Further, as will bedescribed, the optical valves of the present disclosure may achieve thinoptical components with large back working distances. Such componentscan be used in directional backlights, to provide directional displaysincluding autostereoscopic displays. Further, embodiments may provide acontrolled illuminator for the purposes of an efficient autostereoscopicdirectional display device.

Embodiments of the present disclosure may be used in a variety ofoptical systems. The embodiment may include or work with a variety ofprojectors, projection systems, optical components, displays,microdisplays, computer systems, processors, self-contained projectorsystems, visual and/or audiovisual systems and electrical and/or opticaldevices. Aspects of the present disclosure may be used with practicallyany apparatus related to optical and electrical devices, opticalsystems, presentation systems or any apparatus that may contain any typeof optical system. Accordingly, embodiments of the present disclosuremay be employed in optical systems, devices used in visual and/oroptical presentations, visual peripherals and so on and in a number ofcomputing environments.

Before proceeding to the disclosed embodiments in detail, it should beunderstood that the disclosure is not limited in its application orcreation to the details of the particular arrangements shown, becausethe disclosure is capable of other embodiments. Moreover, aspects of thedisclosure may be set forth in different combinations and arrangementsto define embodiments unique in their own right. Also, the terminologyused herein is for the purpose of description and not of limitation.

Directional backlights offer control over the illumination emanatingfrom substantially the entire output surface controlled typicallythrough modulation of independent LED light sources arranged at theinput aperture side of an optical waveguide. Controlling the emittedlight directional distribution can achieve single person viewing for asecurity function, where the display can only be seen by a single viewerfrom a limited range of angles; high electrical efficiency, whereillumination is only provided over a small angular directionaldistribution; alternating left and right eye viewing for time sequentialstereoscopic and autostereoscopic display; and low cost and efficientillumination of color filter array free LCDs.

These and other advantages and features of the present disclosure willbecome apparent to those of ordinary skill in the art upon reading thisdisclosure in its entirety.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments are illustrated by way of example in the accompanyingFIGURES, in which like reference numbers indicate similar parts, and inwhich:

FIG. 1A is a schematic diagram illustrating a front view of lightpropagation in one embodiment of a directional display device, inaccordance with the present disclosure;

FIG. 1B is a schematic diagram illustrating a side view of lightpropagation in one embodiment of the directional display device of FIG.1A, in accordance with the present disclosure;

FIG. 2A is a schematic diagram illustrating in a top view of lightpropagation in another embodiment of a directional display device, inaccordance with the present disclosure;

FIG. 2B is a schematic diagram illustrating light propagation in a frontview of the directional display device of FIG. 2A, in accordance withthe present disclosure;

FIG. 2C is a schematic diagram illustrating light propagation in a sideview of the directional display device of FIG. 2A, in accordance withthe present disclosure;

FIG. 3 is a schematic diagram illustrating in a side view of adirectional display device, in accordance with the present disclosure;

FIG. 4A is schematic diagram illustrating in a front view, generation ofa viewing window in a directional display device and including curvedlight extraction features, in accordance with the present disclosure;

FIG. 4B is a schematic diagram illustrating in a front view, generationof a first and a second viewing window in a directional display deviceand including curved light extraction features, in accordance with thepresent disclosure;

FIG. 5 is a schematic diagram illustrating generation of a first viewingwindow in a directional display device including linear light extractionfeatures, in accordance with the present disclosure;

FIG. 6A is a schematic diagram illustrating one embodiment of thegeneration of a first viewing window in a time multiplexed directionaldisplay device, in accordance with the present disclosure;

FIG. 6B is a schematic diagram illustrating another embodiment of thegeneration of a second viewing window in a time multiplexed directionaldisplay device in a second time slot, in accordance with the presentdisclosure;

FIG. 6C is a schematic diagram illustrating another embodiment of thegeneration of a first and a second viewing window in a time multiplexeddirectional display device, in accordance with the present disclosure;

FIG. 7 is a schematic diagram illustrating an observer trackingautostereoscopic directional display device, in accordance with thepresent disclosure;

FIG. 8 is a schematic diagram illustrating a multi-viewer directionaldisplay device, in accordance with the present disclosure;

FIG. 9 is a schematic diagram illustrating a privacy directional displaydevice, in accordance with the present disclosure;

FIG. 10 is a schematic diagram illustrating in side view, the structureof a directional display device, in accordance with the presentdisclosure;

FIG. 11 is a schematic diagram illustrating in side view, directionaldisplay apparatus including a control system for a directional displaydevice, in accordance with the present disclosure;

FIG. 12 is a schematic diagram illustrating stacked directionalbacklights of a directional display device, in accordance with thepresent disclosure;

FIG. 13 is a schematic diagram illustrating in side view, a directionaldisplay device that provides at least first and second viewing windows,in accordance with the present disclosure;

FIG. 14 is a schematic diagram illustrating stacked directionalbacklights of a directional display device, in accordance with thepresent disclosure;

FIG. 15 is a schematic diagram illustrating in side view, a directionaldisplay device arranged to provide at least first and second viewingwindows, in accordance with the present disclosure;

FIG. 16 is a schematic diagram illustrating stacked directionalbacklights of a directional display device including three directionalbacklights arranged in series to provide respective red, green and blueillumination directions for illumination of a transmissive spatial lightmodulator, in accordance with the present disclosure;

FIG. 17 is a schematic diagram illustrating in side view, a directionaldisplay device including three directional backlights arranged in seriesto provide respective red, green and blue illumination of a transmissivespatial light modulator, in accordance with the present disclosure;

FIG. 18 is a schematic diagram in top view, a detail of the spatiallight modulator of FIG. 16 arranged to achieve efficient illumination ofred, green and blue pixels of the respective spatial light modulator, inaccordance with the present disclosure;

FIG. 19 is a schematic diagram of a directional display device includingtwo directional backlights arranged in series to provide landscape andportrait autostereoscopic viewing, in accordance with the presentdisclosure;

FIG. 20A is a schematic diagram in side view, a directional displaydevice including two directional backlights arranged in series toprovide landscape and portrait autostereoscopic viewing, in accordancewith the present disclosure;

FIG. 20B is a schematic diagram in side view a directional displaydevice including two directional backlights arranged in series with aspatial light modulator, in accordance with the present disclosure;

FIG. 20C is a schematic diagram in side view, and further illustrates adirectional display device including two directional backlights arrangedin series with a spatial light modulator, in accordance with the presentdisclosure;

FIG. 21A is a schematic diagram illustrating tiled directionalbacklights of a directional display device arranged to achieve increasedillumination area, in accordance with the present disclosure;

FIG. 21B is a schematic diagram illustrating in side view, a directionaldisplay device including two tiled directional backlights arranged toachieve increased display area, in accordance with the presentdisclosure;

FIG. 22 is a schematic diagram illustrating an array of tileddirectional backlights including rows of stepped waveguides, inaccordance with the present disclosure;

FIG. 23 is a schematic diagram illustrating tiled directional backlightsof a directional display device arranged to achieve increasedillumination area, in accordance with the present disclosure;

FIG. 24 is a schematic diagram illustrating in side view, tileddirectional backlights of a directional display device arranged toachieve increased display area, in accordance with the presentdisclosure;

FIG. 25 is a schematic diagram illustrating in side view, tileddirectional backlights of a directional display device arranged toachieve increased display area, in accordance with the presentdisclosure;

FIG. 26 is a schematic diagram illustrating in side view, tileddirectional backlights of a directional display device arranged toachieve increased display area, in accordance with the presentdisclosure;

FIG. 27 is a schematic diagram illustrating tiled directional backlightsof a directional display device arranged to achieve increasedillumination area, in accordance with the present disclosure;

FIG. 28A is a schematic diagram illustrating in side view, tileddirectional backlights of a directional display device arranged toachieve increased display area, in accordance with the presentdisclosure;

FIG. 28B is a schematic diagram illustrating in side view, tileddirectional backlights of a directional display device arranged toachieve increased display area, in accordance with the presentdisclosure;

FIG. 28C is a schematic diagram illustrating tiled directionalbacklights of a directional display device arranged to achieve increaseddisplay area, in accordance with the present disclosure;

FIG. 29 is a schematic diagram illustrating an array of directionalbacklights arranged to provide an autostereoscopic directional displaydevice, in accordance with the present disclosure;

FIG. 30 is a schematic diagram illustrating propagation of light in anarray of directional backlights, in accordance with the presentdisclosure;

FIG. 31 is a schematic diagram illustrating further details of lightpropagation in an array of directional backlights and an output Fresnellens of a directional display device, in accordance with the presentdisclosure;

FIG. 32 is a schematic diagram illustrating scanned addressing of anautostereoscopic directional display device in cooperation with an arrayof directional backlights, in accordance with the present disclosure;

FIG. 33 is a schematic diagram illustrating in side view, scannedaddressing of an autostereoscopic directional display device incooperation with an array of directional backlights, in accordance withthe present disclosure;

FIG. 34A is a schematic diagram illustrating in front view, an array oftiled directional backlights to provide an increased illumination area,in accordance with the present disclosure;

FIG. 34B is a schematic diagram illustrating in side view, an array ofdirectional backlights to provide an increased illumination area, inaccordance with the present disclosure;

FIG. 34C is a schematic diagram illustrating in side view, an array ofdirectional backlights to provide an increased illumination area, inaccordance with the present disclosure;

FIG. 34D is a schematic diagram illustrating in front view, adirectional backlight including linear light extraction features and aplanar diffractive reflector arranged to provide collimation of incidentlight, in accordance with the present disclosure;

FIG. 34E is a schematic diagram illustrating in front view, imaging by adirectional backlight including curved light extraction features and aplanar diffractive reflector arranged to provide focusing of incidentlight, in accordance with the present disclosure;

FIG. 34F is a schematic diagram illustrating light propagation for lightoutput in a tiled array of directional backlights including adiffractive reflector, in accordance with the present disclosure;

FIG. 34G is a schematic diagram illustrating in front view a tiled arrayof directional backlights including diffractive reflectors, inaccordance with the present disclosure;

FIG. 35 is a schematic diagram illustrating in front view an array ofdirectional backlights to provide an increased illumination area, inaccordance with the present disclosure;

FIG. 36 is a schematic diagram illustrating in front view an array ofdirectional backlights to provide an increased illumination area, inaccordance with the present disclosure;

FIG. 37 is a schematic diagram illustrating in front view, an array ofdirectional backlights to provide an increased illumination area, inaccordance with the present disclosure;

FIG. 38 is a schematic diagram illustrating an embodiment in whichdirectional backlights incorporate light blocking layers at theinterface between separate stepped waveguides, in accordance with thepresent disclosure;

FIG. 39 is a schematic diagram illustrating in front view, an array ofdirectional backlights to provide an increased illumination area, inaccordance with the present disclosure;

FIG. 40 is a schematic diagram illustrating in side view the boundarybetween two stepped waveguides of an array of directional backlights, inaccordance with the present disclosure;

FIG. 41 is a schematic diagram illustrating in side view, the boundarybetween two stepped waveguides of an array of directional backlights, inaccordance with the present disclosure;

FIG. 42 is a schematic diagram illustrating in side view, first andsecond ends of a stepped waveguide, in accordance with the presentdisclosure;

FIG. 43 is a schematic diagram illustrating in side view, first andsecond ends of a stepped waveguide assembled in an array of directionalbacklights, in accordance with the present disclosure;

FIG. 44A is a schematic diagram illustrating in side view, a steppedwaveguide suitable for an array of directional backlights, in accordancewith the present disclosure;

FIG. 44B is a schematic diagram illustrating in side view, first andsecond ends of a stepped waveguide assembled in an array of directionalbacklights, in accordance with the present disclosure;

FIG. 45 is a schematic diagram illustrating in side view, first andsecond ends of a stepped waveguide including diffractive reflectors, inaccordance with the present disclosure;

FIG. 46 is a schematic diagram illustrating in side view, an array ofdirectional backlights, in accordance with the present disclosure;

FIG. 47 is a schematic diagram illustrating in front view, an array ofdirectional backlights, in accordance with the present disclosure;

FIG. 48A is a schematic diagram illustrating in side view, tileddirectional backlights including a grating coupler, in accordance withthe present disclosure;

FIG. 48B is a schematic diagram illustrating in side view, directionalbacklights including a grating coupler, in accordance with the presentdisclosure;

FIG. 49 is a schematic diagram illustrating in side view, a directionalbacklights including a prismatic coupler, in accordance with the presentdisclosure;

FIG. 50 is a schematic diagram illustrating in front view, thearrangement of the viewing zones from an autostereoscopic displayincluding a single illumination region with an observer at the windowplane, in accordance with the present disclosure;

FIG. 51 is a schematic diagram illustrating in front view, thearrangement of the near viewing zones from an autostereoscopicdirectional display device including multiple illumination regions withan observer at the window plane, in accordance with the presentdisclosure;

FIG. 52 is a schematic diagram illustrating in front view, thearrangement of the near viewing zones from an autostereoscopicdirectional display device including multiple illumination regions withan observer between the window plane and the display, in accordance withthe present disclosure;

FIG. 53 is a schematic diagram illustrating in front view, thearrangement of the near viewing regions from an autostereoscopicdirectional display device including multiple illumination regions for amoving observer between the window plane and the display, in accordancewith the present disclosure;

FIG. 54 is a schematic diagram illustrating a limit of longitudinalviewing freedom for an autostereoscopic directional display deviceincluding multiple illumination regions, in accordance with the presentdisclosure;

FIG. 55 is a schematic diagram illustrating a front view of a waveguideincluding first and second light reflecting sides for a firstillumination arrangement, in accordance with the present disclosure;

FIG. 56 is a schematic diagram illustrating a front view of a waveguideincluding first and second light reflecting sides for a secondillumination arrangement, in accordance with the present disclosure;

FIG. 57 is a schematic diagram illustrating graphs of display luminanceacross the width of the waveguide for various illumination arrangements,in accordance with the present disclosure;

FIG. 58 is a schematic diagram illustrating a front view of a waveguideincluding first and second light reflecting sides for a thirdillumination arrangement, in accordance with the present disclosure; and

FIG. 59 is a schematic diagram illustrating graphs of display luminanceacross the width of the waveguide for various illumination arrangements,in accordance with the present disclosure.

FIG. 60 is a schematic diagram illustrating a first arrangement of adiffractive mirror in accordance with the present disclosure;

FIG. 61 is a schematic diagram illustrating a further arrangement of adiffractive mirror in accordance with the present disclosure;

FIG. 62 is a schematic diagram illustrating a method to form aholographic mirror on a waveguide in accordance with the presentdisclosure; and

FIG. 63 is a schematic diagram illustrating the end view of aholographic mirror in accordance with the present disclosure.

DETAILED DESCRIPTION

Time multiplexed autostereoscopic displays can advantageously improvethe spatial resolution of autostereoscopic display by directing lightfrom all of the pixels of a spatial light modulator to a first viewingwindow in a first time slot, and all of the pixels to a second viewingwindow in a second time slot. Thus an observer with eyes arranged toreceive light in first and second viewing windows will see a fullresolution image across the whole of the display over multiple timeslots. Time multiplexed displays can advantageously achieve directionalillumination by directing an illuminator array through a substantiallytransparent time multiplexed spatial light modulator using directionaloptical elements, wherein the directional optical elements substantiallyform an image of the illuminator array in the window plane.

For the purposes of the present embodiments, an optical window definesthe illumination profile that is produced by a single light emittingelement of an array of light emitting elements in cooperation with theoptical system. A viewing window defines the illumination profile thatis seen by one eye of a viewer and may thus include multiple opticalwindows. Thus an observer's eye placed in a viewing window may see asingle image across at least part of the area of a spatial lightmodulator. The window plane is a nominal plane at which an image of thelight emitting elements is formed, the separation of the window planefrom the spatial light modulator being the nominal viewing distance ofthe display system.

The uniformity of the viewing windows may be advantageously independentof the arrangement of pixels in the spatial light modulator.Advantageously, such displays can provide observer tracking displayswhich have low flicker, with low levels of cross talk for a movingobserver.

To achieve high uniformity in the window plane, it is desirable toprovide an array of illumination elements that have a high spatialuniformity. The illuminator elements of the time sequential illuminationsystem may be provided, for example, by pixels of a spatial lightmodulator with size approximately 100 micrometers in combination with alens array. However, such pixels suffer from similar difficulties as forspatially multiplexed displays. Further, such devices may have lowefficiency and higher cost, requiring additional display components.

High window plane uniformity can be conveniently achieved withmacroscopic illuminators, for example, an array of LEDs in combinationwith homogenizing and diffusing optical elements that are typically ofsize 1 mm or greater. However, the increased size of the illuminatorelements means that the size of the directional optical elementsincreases proportionately. For example, a 16 mm wide illuminator imagedto a 65 mm wide viewing window (that may include multiple opticalwindows, typically between five and ten optical windows in displays thatcan achieve low flicker observer tracking) may require a 200 mm backworking distance. Thus, the increased thickness of the optical elementscan prevent useful application, for example, to mobile displays, orlarge area displays.

Addressing the aforementioned shortcomings, optical valves as describedin commonly-owned U.S. patent application Ser. No. 13/300,293advantageously can be arranged in combination with fast switchingtransmissive spatial light modulators to achieve time multiplexedautostereoscopic illumination in a thin package while providing highresolution images with flicker free observer tracking and low levels ofcross talk. Described is a one dimensional array of viewing positions,or viewing windows, that can display different images in a first,typically horizontal, direction, but contain the same images when movingin a second, typically vertical, direction.

Conventional non-imaging display backlights commonly employ opticalwaveguides and have edge illumination from light sources such as LEDs.However, it should be appreciated that there are many fundamentaldifferences in the function, design, structure, and operation betweensuch conventional non-imaging display backlights and the imagingdirectional backlights discussed in the present disclosure.

Generally, for example, in accordance with the present disclosure,imaging directional backlights are arranged to direct the illuminationfrom multiple light sources through a display panel to respectivemultiple viewing windows in at least one axis. Each viewing window issubstantially formed as an image in at least one axis of a light sourceby the imaging system of the imaging directional backlight. An imagingsystem may be formed between multiple light sources and the respectiveoptical windows. In this manner, the light from each of the multiplelight sources is substantially not visible for an observer's eye outsideof the respective viewing window.

In contradistinction, conventional non-imaging backlights or lightguiding plates (LGPs) are used for illumination of 2D displays. See,e.g., Kälil Käläntär et al., Backlight Unit With Double Surface LightEmission, J. Soc. Inf. Display, Vol. 12, Issue 4, pp. 379-387 (December2004). Non-imaging backlights are typically arranged to direct theillumination from multiple light sources through a display panel into asubstantially common viewing zone for each of the multiple light sourcesto achieve wide viewing angle and high display uniformity. Thusnon-imaging backlights do not form viewing windows. In this manner, thelight from each of the multiple light sources may be visible for anobserver's eye at substantially all positions across the viewing zone.Such conventional non-imaging backlights may have some directionality,for example, to increase screen gain compared to Lambertianillumination, which may be provided by brightness enhancement films suchas BEF™ from 3M. However, such directionality may be substantially thesame for each of the respective light sources. Thus, for these reasonsand others that should be apparent to persons of ordinary skill,conventional non-imaging backlights are different to imaging directionalbacklights. Edge lit non-imaging backlight illumination structures maybe used in liquid crystal display systems such as those seen in 2DLaptops, Monitors and TVs. Light propagates from the edge of a lossywaveguide which may include sparse features; typically localindentations in the surface of the guide which cause light to be lostregardless of the propagation direction of the light.

One example of an imaging directional backlight is an optical valve thatmay employ a folded optical system. Light may propagate substantiallywithout loss in one direction through the optical valve, may be incidenton an imaging reflector, and may counter-propagate such that the lightmay be extracted by reflection off tilted light extraction features, anddirected to viewing windows as described in patent application Ser. No.13/300,293, which is herein incorporated by reference in its entirety.

As used herein, examples of an imaging directional backlight include astepped waveguide imaging directional backlight, a folded imagingdirectional backlight, a wedge type directional backlight, or an opticalvalve.

Additionally, as used herein, a stepped waveguide imaging directionalbacklight may be an optical valve. A stepped waveguide is a waveguidefor an imaging directional backlight including a waveguide for guidinglight, further including a first light guiding surface; and a secondlight guiding surface, opposite the first light guiding surface, furtherincluding a plurality of light guiding features interspersed with aplurality of extraction features arranged as steps.

Moreover, as used, a folded imaging directional backlight may be atleast one of a wedge type directional backlight, or an optical valve.

In operation, light may propagate within an exemplary optical valve in afirst direction from an input side to a reflective side and may betransmitted substantially without loss. Light may be reflected at thereflective side and propagates in a second direction substantiallyopposite the first direction. As the light propagates in the seconddirection, the light may be incident on light extraction features, whichare operable to redirect the light outside the optical valve. Stateddifferently, the optical valve generally allows light to propagate inthe first direction and may allow light to be extracted whilepropagating in the second direction.

The optical valve may achieve time sequential directional illuminationof large display areas. Additionally, optical elements may be employedthat are thinner than the back working distance of the optical elementsto direct light from macroscopic illuminators to a window plane. Suchdisplays may use an array of light extraction features arranged toextract light counter propagating in a substantially parallel waveguide.

Thin imaging directional backlight implementations for use with LCDshave been proposed and demonstrated by 3M, for example U.S. Pat. No.7,528,893; by Microsoft, for example U.S. Pat. No. 7,970,246 which maybe referred to herein as a “wedge type directional backlight;” by RealD,for example U.S. patent application Ser. No. 13/300,293 which may bereferred to herein as an “optical valve” or “optical valve directionalbacklight,” all of which are herein incorporated by reference in theirentirety.

The present disclosure provides stepped waveguide imaging directionalbacklights in which light may reflect back and forth between theinternal faces of, for example, a stepped waveguide which may include afirst side and a first set of features. As the light travels along thelength of the stepped waveguide, the light may not substantially changeangle of incidence with respect to the first side and first set ofsurfaces and so may not reach the critical angle of the medium at theseinternal faces. Light extraction may be advantageously achieved by asecond set of surfaces (the step “risers”) that are inclined to thefirst set of surfaces (the step “treads”). Note that the second set ofsurfaces may not be part of the light guiding operation of the steppedwaveguide, but may be arranged to provide light extraction from thestructure. By contrast, a wedge type imaging directional backlight mayallow light to guide within a wedge profiled waveguide having continuousinternal surfaces. The optical valve is thus not a wedge type imagingdirectional backlight.

FIG. 1A is a schematic diagram illustrating a front view of lightpropagation in one embodiment of a directional display device, and FIG.1B is a schematic diagram illustrating a side view of light propagationin the directional display device of FIG. 1A.

FIG. 1A illustrates a front view in the xy plane of a directionalbacklight of a directional display device, and includes an illuminatorarray 15 which may be used to illuminate a stepped waveguide 1.Illuminator array 15 includes illuminator elements 15 a throughilluminator element 15 n (where n is an integer greater than one). Inone example, the stepped waveguide 1 of FIG. 1A may be a stepped,display sized waveguide 1. Illumination elements 15 a through 15 n arelight sources that may be light emitting diodes (LEDs). Although LEDsare discussed herein as illuminator elements 15 a-15 n, other lightsources may be used such as, but not limited to, diode sources,semiconductor sources, laser sources, local field emission sources,organic emitter arrays, and so forth. Additionally, FIG. 1B illustratesa side view in the xz plane, and includes illuminator array 15, SLM(spatial light modulator) 48, extraction features 12, guiding features10, and stepped waveguide 1, arranged as shown. The side view providedin FIG. 1B is an alternative view of the front view shown in FIG. 1A.Accordingly, the illuminator array 15 of FIGS. 1A and 1B corresponds toone another and the stepped waveguide 1 of FIGS. 1A and 1B maycorrespond to one another.

Further, in FIG. 1B, the stepped waveguide 1 may have an input end 2that is thin and a reflective end 4 that is thick. Thus the waveguide 1extends between the input end 2 that receives input light and thereflective end 4 that reflects the input light back through thewaveguide 1. The length of the input end 2 in a lateral direction acrossthe waveguide is greater than the height of the input end 2. Theilluminator elements 15 a-15 n are disposed at different input positionsin a lateral direction across the input end 2.

The waveguide 1 has first and second, opposed guide surfaces extendingbetween the input end 2 and the reflective end 4 for guiding lightforwards and back along the waveguide 1 by total internal reflection.The first guide surface is planar. The second guide surface has aplurality of light extraction features 12 facing the reflective end 4and inclined to reflect at least some of the light guided back throughthe waveguide 1 from the reflective end in directions that break thetotal internal reflection at the first guide surface and allow outputthrough the first guide surface, for example, upwards in FIG. 1B, thatis supplied to the SLM 48.

In this example, the light extraction features 12 are reflective facets,although other reflective features could be used. The light extractionfeatures 12 do not guide light through the waveguide, whereas theintermediate regions of the second guide surface intermediate the lightextraction features 12 guide light without extracting it. Those regionsof the second guide surface are planar and may extend parallel to thefirst guide surface, or at a relatively low inclination. The lightextraction features 12 extend laterally to those regions so that thesecond guide surface has a stepped shape including of the lightextraction features 12 and intermediate regions. The light extractionfeatures 12 are oriented to reflect light from the light sources, afterreflection from the reflective end 4, through the first guide surface.

The light extraction features 12 are arranged to direct input light fromdifferent input positions in the lateral direction across the input endin different directions relative to the first guide surface that aredependent on the input position. As the illumination elements 15 a-15 nare arranged at different input positions, the light from respectiveillumination elements 15 a-15 n is reflected in those differentdirections. In this manner, each of the illumination elements 15 a-15 ndirects light into a respective optical window in output directionsdistributed in the lateral direction in dependence on the inputpositions. The lateral direction across the input end 2 in which theinput positions are distributed corresponds with regard to the outputlight to a lateral direction to the normal to the first guide surface.The lateral directions as defined at the input end 2 and with regard tothe output light remain parallel in this embodiment where thedeflections at the reflective end 4 and the first guide surface aregenerally orthogonal to the lateral direction. Under the control of acontrol system, the illuminator elements 15 a-15 n may be selectivelyoperated to direct light into a selectable optical window. The opticalwindows may be used individually or in groups as viewing windows.

The SLM 48 extends across the waveguide is transmissive and modulatesthe light passing therethrough. Although the SLM 48 may be a liquidcrystal display (LCD) but this is merely by way of example, and otherspatial light modulators or displays may be used including LCOS, DLPdevices, and so forth, as this illuminator may work in reflection. Inthis example, the SLM 48 is disposed across the first guide surface ofthe waveguide and modulates the light output through the first guidesurface after reflection from the light extraction features 12.

The operation of a directional display device that may provide a onedimensional array of viewing windows is illustrated in front view inFIG. 1A, with its side profile shown in FIG. 1B. In operation, in FIGS.1A and 1B, light may be emitted from an illuminator array 15, such as anarray of illuminator elements 15 a through 15 n, located at differentpositions, y, along the surface of thin end side 2, x=0, of the steppedwaveguide 1. The light may propagate along +x in a first direction,within the stepped waveguide 1, while at the same time, the light mayfan out in the xy plane and upon reaching the far curved end side 4, maysubstantially or entirely fill the curved end side 4. While propagating,the light may spread out to a set of angles in the xz plane up to, butnot exceeding the critical angle of the guide material. The extractionfeatures 12 that link the guiding features 10 of the bottom side of thestepped waveguide 1 may have a tilt angle greater than the criticalangle and hence may be missed by substantially all light propagatingalong +x in the first direction, ensuring the substantially losslessforward propagation.

Continuing the discussion of FIGS. 1A and 1B, the curved end side 4 ofthe stepped waveguide 1 may be made reflective, typically by beingcoated with a reflective material such as, for example, silver, althoughother reflective techniques may be employed. Light may therefore beredirected in a second direction, back down the guide in the directionof −x and may be substantially collimated in the xy or display plane.The angular spread may be substantially preserved in the xz plane aboutthe principal propagation direction, which may allow light to hit theriser edges and reflect out of the guide. In an embodiment withapproximately 45 degree tilted extraction features 12, light may beeffectively directed approximately normal to the xy display plane withthe xz angular spread substantially maintained relative to thepropagation direction. This angular spread may be increased when lightexits the stepped waveguide 1 through refraction, but may be decreasedsomewhat dependent on the reflective properties of the extractionfeatures 12.

In some embodiments with uncoated extraction features 12, reflection maybe reduced when total internal reflection (TIR) fails, squeezing the xzangular profile and shifting off normal. However, in other embodimentshaving silver coated or metallized extraction features, the increasedangular spread and central normal direction may be preserved. Continuingthe description of the embodiment with silver coated extractionfeatures, in the xz plane, light may exit the stepped waveguide 1approximately collimated and may be directed off normal in proportion tothe y-position of the respective illuminator element 15 a-15 n inilluminator array 15 from the input edge center. Having independentilluminator elements 15 a-15 n along the input edge 2 then enables lightto exit from the entire first light directing side 6 and propagate atdifferent external angles, as illustrated in FIG. 1A.

Illuminating a spatial light modulator (SLM) 48 such as a fast liquidcrystal display (LCD) panel with such a device may achieveautostereoscopic 3D as shown in top view or yz-plane viewed from theilluminator array 15 end in FIG. 2A, front view in FIG. 2B and side viewin FIG. 2C. FIG. 2A is a schematic diagram illustrating in a top view,propagation of light in a directional display device, FIG. 2B is aschematic diagram illustrating in a front view, propagation of light ina directional display device, and FIG. 2C is a schematic diagramillustrating in side view propagation of light in a directional displaydevice. As illustrated in FIGS. 2A, 2B, and 2C, a stepped waveguide 1may be located behind a fast (e.g., greater than 100 Hz) LCD panel SLM48 that displays sequential right and left eye images. Insynchronization, specific illuminator elements 15 a through 15 n ofilluminator array 15 (where n is an integer greater than one) may beselectively turned on and off, providing illuminating light that entersright and left eyes substantially independently by virtue of thesystem's directionality. In the simplest case, sets of illuminatorelements of illuminator array 15 are turned on together, providing a onedimensional viewing window 26 or an optical pupil with limited width inthe horizontal direction, but extended in the vertical direction, inwhich both eyes horizontally separated may view a left eye image, andanother viewing window 44 in which a right eye image may primarily beviewed by both eyes, and a central position in which both the eyes mayview different images. In this way, 3D may be viewed when the head of aviewer is approximately centrally aligned. Movement to the side awayfrom the central position may result in the scene collapsing onto a 2Dimage.

The reflective end 4 may have positive optical power in the lateraldirection across the waveguide. In embodiments in which typically thereflective end 4 has positive optical power, the optical axis may bedefined with reference to the shape of the reflective end 4, for examplebeing a line that passes through the centre of curvature of thereflective end 4 and coincides with the axis of reflective symmetry ofthe end 4 about the x-axis. In the case that the reflecting surface 4 isflat, the optical axis may be similarly defined with respect to othercomponents having optical power, for example the light extractionfeatures 12 if they are curved, or the Fresnel lens 62 described below.The optical axis 238 is typically coincident with the mechanical axis ofthe waveguide 1. The cylindrical reflecting surface at end 4 maytypically be a spherical profile to optimize performance for on-axis andoff-axis viewing positions. Other profiles may be used.

FIG. 3 is a schematic diagram illustrating in side view a directionaldisplay device. Further, FIG. 3 illustrates additional detail of a sideview of the operation of a stepped waveguide 1, which may be atransparent material. The stepped waveguide 1 may include an illuminatorinput side 2, a reflective side 4, a first light directing side 6 whichmay be substantially planar, and a second light directing side 8 whichincludes guiding features 10 and light extraction features 12. Inoperation, light rays 16 from an illuminator element 15 c of anilluminator array 15 (not shown in FIG. 3), that may be an addressablearray of LEDs for example, may be guided in the stepped waveguide 1 bymeans of total internal reflection by the first light directing side 6and total internal reflection by the guiding feature 10, to thereflective side 4, which may be a mirrored surface. Although reflectiveside 4 may be a mirrored surface and may reflect light, it may in someembodiments also be possible for light to pass through reflective side4.

Continuing the discussion of FIG. 3, light ray 18 reflected by thereflective side 4 may be further guided in the stepped waveguide 1 bytotal internal reflection at the reflective side 4 and may be reflectedby extraction features 12. Light rays 18 that are incident on extractionfeatures 12 may be substantially deflected away from guiding modes ofthe stepped waveguide 1 and may be directed, as shown by ray 20, throughthe side 6 to an optical pupil that may form a viewing window 26 of anautostereoscopic display. The width of the viewing window 26 may bedetermined by at least the size of the illuminator, output designdistance and optical power in the side 4 and extraction features 12. Theheight of the viewing window may be primarily determined by thereflection cone angle of the extraction features 12 and the illuminationcone angle input at the input side 2. Thus each viewing window 26represents a range of separate output directions with respect to thesurface normal direction of the spatial light modulator 48 thatintersect with a plane at the nominal viewing distance.

FIG. 4A is a schematic diagram illustrating in front view a directionaldisplay device which may be illuminated by a first illuminator elementand including curved light extraction features. Further, FIG. 4A showsin front view further guiding of light rays from illuminator element 15c of illuminator array 15, in the stepped waveguide 1 having an opticalaxis 28. In FIG. 4A, the directional backlight may include the steppedwaveguide 1 and the light source illuminator array 15. Each of theoutput rays are directed from the input side 2 towards the same viewingwindow 26 from the respective illuminator 15 c. The light rays of FIG.4A may exit the reflective side 4 of the stepped waveguide 1. As shownin FIG. 4A, ray 16 may be directed from the illuminator element 15 ctowards the reflective side 4. Ray 18 may then reflect from a lightextraction feature 12 and exit the reflective side 4 towards the viewingwindow 26. Thus light ray 30 may intersect the ray 20 in the viewingwindow 26, or may have a different height in the viewing window as shownby ray 32. Additionally, in various embodiments, sides 22, 24 of thewaveguide 1 may be transparent, mirrored, or blackened surfaces.Continuing the discussion of FIG. 4A, light extraction features 12 maybe elongate, and the orientation of light extraction features 12 in afirst region 34 of the light directing side 8 (light directing side 8shown in FIG. 3, but not shown in FIG. 4A) may be different to theorientation of light extraction features 12 in a second region 36 of thelight directing side 8. Similar to other embodiments discussed herein,for example as illustrated in FIG. 3, the light extraction features ofFIG. 4A may alternate with the guiding features 10. As illustrated inFIG. 4A, the stepped waveguide 1 may include a reflective surface onreflective side 4. In one embodiment, the reflective end of the steppedwaveguide 1 may have positive optical power in a lateral directionacross the stepped waveguide 1.

In another embodiment, the light extraction features 12 of eachdirectional backlight may have positive optical power in a lateraldirection across the waveguide.

In another embodiment, each directional backlight may include lightextraction features 12 which may be facets of the second guide surface.The second guide surface may have regions alternating with the facetsthat may be arranged to direct light through the waveguide withoutsubstantially extracting it.

FIG. 4B is a schematic diagram illustrating in front view a directionaldisplay device which may illuminated by a second illuminator element.Further, FIG. 4B shows the light rays 40, 42 from a second illuminatorelement 15 h of the illuminator array 15. The curvature of thereflective surface on the side 4 and the light extraction features 12cooperatively produce a second viewing window 44 laterally separatedfrom the viewing window 26 with light rays from the illuminator element15 h.

Advantageously, the arrangement illustrated in FIG. 4B may provide areal image of the illuminator element 15 c at a viewing window 26 inwhich the real image may be formed by cooperation of optical power inreflective side 4 and optical power which may arise from differentorientations of elongate light extraction features 12 between regions 34and 36, as shown in FIG. 4A. The arrangement of FIG. 4B may achieveimproved aberrations of the imaging of illuminator element 15 c tolateral positions in viewing window 26. Improved aberrations may achievean extended viewing freedom for an autostereoscopic display whileachieving low cross talk levels.

FIG. 5 is a schematic diagram illustrating in front view an embodimentof a directional display device having substantially linear lightextraction features. Further, FIG. 5 shows a similar arrangement ofcomponents to FIG. 1 (with corresponding elements being similar), withone of the differences being that the light extraction features 12 aresubstantially linear and parallel to each other. Advantageously, such anarrangement may provide substantially uniform illumination across adisplay surface and may be more convenient to manufacture than thecurved extraction features of FIG. 4A and FIG. 4B. The optical axis 321of the directional waveguide 1 may be the optical axis direction of thesurface at side 4. The optical power of the side 4 is arranged to beacross the optical axis direction, thus rays incident on the side 4 willhave an angular deflection that varies according to the lateral offset319 of the incident ray from the optical axis 321.

FIG. 6A is a schematic diagram illustrating one embodiment of thegeneration of a first viewing window in a time multiplexed imagingdirectional display device in a first time slot, FIG. 6B is a schematicdiagram illustrating another embodiment of the generation of a secondviewing window in a time multiplexed imaging directional backlightapparatus in a second time slot, and FIG. 6C is a schematic diagramillustrating another embodiment of the generation of a first and asecond viewing window in a time multiplexed imaging directional displaydevice. Further, FIG. 6A shows schematically the generation of viewingwindow 26 from stepped waveguide 1. Illuminator element group 31 inilluminator array 15 may provide a light cone 17 directed towards aviewing window 26. FIG. 6B shows schematically the generation of viewingwindow 44. Illuminator element group 33 in illuminator array 15 mayprovide a light cone 19 directed towards viewing window 44. Incooperation with a time multiplexed display, windows 26 and 44 may beprovided in sequence as shown in FIG. 6C. If the image on a spatiallight modulator 48 (not shown in FIGS. 6A, 6B, 6C) is adjusted incorrespondence with the light direction output, then an autostereoscopicimage may be achieved for a suitably placed viewer. Similar operationcan be achieved with all the imaging directional backlights describedherein. Note that illuminator element groups 31, 33 each include one ormore illumination elements from illumination elements 15 a to 15 n,where n is an integer greater than one.

FIG. 7 is a schematic diagram illustrating one embodiment of an observertracking autostereoscopic display apparatus including a time multiplexeddirectional display device. As shown in FIG. 7, selectively turning onand off illuminator elements 15 a to 15 n along axis 29 provides fordirectional control of viewing windows. The head 45 position may bemonitored with a camera, motion sensor, motion detector, or any otherappropriate optical, mechanical or electrical means, and the appropriateilluminator elements of illuminator array 15 may be turned on and off toprovide substantially independent images to each eye irrespective of thehead 45 position. The head tracking system (or a second head trackingsystem) may provide monitoring of more than one head 45, 47 (head 47 notshown in FIG. 7) and may supply the same left and right eye images toeach viewers' left and right eyes providing 3D to all viewers. Againsimilar operation can be achieved with all the imaging directionalbacklights described herein.

FIG. 8 is a schematic diagram illustrating one embodiment of amulti-viewer directional display device as an example including animaging directional backlight. As shown in FIG. 8, at least two 2Dimages may be directed towards a pair of viewers 45, 47 so that eachviewer may watch a different image on the spatial light modulator 48.The two 2D images of FIG. 8 may be generated in a similar manner asdescribed with respect to FIG. 7 in that the two images would bedisplayed in sequence and in synchronization with sources whose light isdirected toward the two viewers. One image is presented on the spatiallight modulator 48 in a first phase, and a second image is presented onthe spatial light modulator 48 in a second phase different from thefirst phase. In correspondence with the first and second phases, theoutput illumination is adjusted to provide first and second viewingwindows 26, 44 respectively. An observer with both eyes in viewingwindow 26 will perceive a first image while an observer with both eyesin viewing window 44 will perceive a second image.

FIG. 9 is a schematic diagram illustrating a privacy directional displaydevice which includes an imaging directional backlight. 2D displaysystems may also utilize directional backlighting for security andefficiency purposes in which light may be primarily directed at the eyesof a first viewer 45 as shown in FIG. 9. Further, as illustrated in FIG.9, although first viewer 45 may be able to view an image on device 50,light is not directed towards second viewer 47. Thus second viewer 47 isprevented from viewing an image on device 50. Each of the embodiments ofthe present disclosure may advantageously provide autostereoscopic, dualimage or privacy display functions.

FIG. 10 is a schematic diagram illustrating in side view the structureof a time multiplexed directional display device as an example includingan imaging directional backlight. Further, FIG. 10 shows in side view anautostereoscopic directional display device, which may include thestepped waveguide 1 and a Fresnel lens 62 arranged to provide theviewing window 26 for a substantially collimated output across thestepped waveguide 1 output surface. A vertical diffuser 68 may bearranged to extend the height of the viewing window 26 further. Thelight may then be imaged through the spatial light modulator 48. Theilluminator array 15 may include light emitting diodes (LEDs) that may,for example, be phosphor converted blue LEDs, or may be separate RGBLEDs. Alternatively, the illuminator elements in illuminator array 15may include a uniform light source and spatial light modulator arrangedto provide separate illumination regions. Alternatively the illuminatorelements may include laser light source(s). The laser output may bedirected onto a diffuser by means of scanning, for example, using agalvo or MEMS scanner. In one example, laser light may thus be used toprovide the appropriate illuminator elements in illuminator array 15 toprovide a substantially uniform light source with the appropriate outputangle, and further to provide reduction in speckle. Alternatively, theilluminator array 15 may be an array of laser light emitting elements.Additionally in one example, the diffuser may be a wavelength convertingphosphor, so that illumination may be at a different wavelength to thevisible output light.

The above description relates to display devices including a singledirectional backlight. There will now be described some display devicesincluding plural directional backlights that may in some cases bestacked and in some cases be tiled. However, the individual directionalbacklights are based on and incorporate the structures of FIGS. 1 to 10above. Accordingly, except for the modifications and/or additionalfeatures which will now be described, the above description applies tothe following display devices but for brevity will not be repeated.

FIG. 11 is a schematic diagram illustrating a directional displayapparatus including a display device and a control system. Thearrangement and operation of the control system will now be describedand may be applied, with changes as necessary, to each of the displaydevices disclosed herein.

The directional display device includes three directional backlights1903, 1905, 1907 in this example, although in general there may be anynumber of directional backlights, such as one, two, three, four, five,and so forth. Each directional backlight 1903, 1905, 1907 includes arespective illuminator array 1913, 1915, 1917. The control system isarranged to selectively operate the illumination elements of theilluminator arrays 1913, 1915, 1917 to direct light into selectableviewing windows.

Each directional backlight 1903, 1905, 1907 includes a waveguide whichmay be arranged as in the embodiments described below. A Fresnel lens 62may be provided to direct collimated output light substantially from thedirectional backlights 1903, 1905, 1907 to the viewing windows, thuspupillating the display output across the output of the directionalbacklights 1903, 1905, 1907 so that viewing windows from each backlight1903, 1905, 1907 substantially overlap in a window plane. A transmissivespatial light modulator (SLM) 48 may be arranged to receive the lightfrom the directional backlights 1903, 1905, 1907.

Further a diffuser 68 may be provided to substantially remove Moirébeating between the directional backlights 1903, 1905, 1907 and thepixels of the SLM 48 as well as the Fresnel lens structure.

The control system may include a sensor system arranged to detect theposition of the observer 99 relative to the display device 100. Thesensor system may include a position sensor 70, such as a camera, and ahead position measurement system 72 that may, for example, include acomputer vision image processing system.

In FIG. 11, the position sensor 70 may include known sensors includingthose with cameras and image processing units arranged to detect theposition of observer faces. Position sensor 70 may further include astereo sensor arranged to improve the measure of longitudinal positioncompared to a monoscopic camera. Alternatively position sensor 70 mayinclude measurement of eye spacing to give a measure of requiredplacement of respective arrays of viewing windows from tiles of thedirectional display.

The control system may further include an illumination controller 74 andan image controller 76 that are both supplied with the detected positionof the observer supplied from the head position measurement system 72.

The illumination controller 74 selectively operates the illuminatorelements 15 to direct light to into the viewing windows 26 incooperation with waveguide 1. The illumination controller 74 selects theilluminator elements 15 to be operated in dependence on the position ofthe observer detected by the head position measurement system 72, sothat the viewing windows 26 into which light is directed are inpositions corresponding to the left and right eyes of the observer 99.In this manner, the lateral output directionality of the waveguide 1corresponds with the observer position.

The image controller 76 controls the SLM 48 to display images. Toprovide an autosterescopic display, the image controller 76 and theillumination controller 74 may operate as follows. The image controller76 controls the SLM 48 to display temporally multiplexed left and righteye images. The illumination controller 74 operate the light sources 15to direct light into viewing windows in positions corresponding to theleft and right eyes of an observer synchronously with the display ofleft and right eye images. In this manner, an autostereoscopic effect isachieved using a time division multiplexing technique.

In operation, light cones 1971, 1973, 1975 may be produced by respectivelight emitting element illuminator arrays 1913, 1915, 1917 andrespective aligned directional backlights 1903, 1905, 1907. As shown inFIG. 11, the light cones 1971, 1973, 1975 direct light to a viewingwindow 26. Thus the respective illumination of arrays 1913, 1915, 1917can be modified in response to lateral, vertical (out of page) andlongitudinal observer movement.

Advantageously, the light emitting element illuminator arrays 1913,1915, 1917 of such tiled arrays of waveguides can be addressed toachieve extended longitudinal viewing freedom for tracked observers aswill be described below.

In the above embodiments, the image controller 76 may use the observerlocation data from position sensor 70 and head position measurementsystem 72 to achieve an image display that varies in response to theobserver 99 location. Advantageously this may be used to provide a “lookaround” facility in which, for example, the image perspective displayedon spatial light modulator 48 may be varied in response to movement ofthe observer 99.

In an illustrative embodiment in which the spatial light modulator 48uses a liquid crystal material, and is line by line addressed, theelectro optic response characteristics of the LC material may beimportant. Furthermore the pulsed illumination may interact with thescanning and the LC response in such a way that may result in differentappearances of pixels located at different spatial positions on thespatial light modulator 48 even if they were addressed with the sameoriginal data. This effect may be eliminated by pre-processing the rawimage data to make a correction. A modification of image data may alsobe made to compensate for predicated crosstalk between left and rightviews.

Further advantageously the knowledge of the observer 99 location may beused to provide a more effective adjustment of the image data to spatiallight modulator 48 in order to compensate for the effects describedabove.

FIG. 12 is a schematic diagram illustrating stacked directionalbacklights of a directional display device including at least a firstand second stepped waveguide arranged in series and FIG. 13 is aschematic diagram illustrating in side view a directional display deviceincorporating the stacked directional backlights of FIG. 12. A firstembodiment may be provided by a stack of two stepped waveguides such asstepped waveguides 100, 104 and respective light source arrays 102, 106arranged in series as shown schematically in FIG. 12 and in side view inFIG. 13. A first directional backlight may include the stepped waveguide100 and the light source array 102 and a second directional backlightmay include the stepped waveguide 104 and the light source illuminatorarray 106. The first and second directional backlight may be stackedbehind a spatial light modulator 48. Further as illustrated in FIG. 12,the first and second directional backlights may include a reflectivesurface. In FIG. 12, the reflective surface is on the curved end of thefirst and second directional backlights. In one embodiment, thereflective surface or reflective end of either one or both of thestepped waveguides 100, 104 may have positive optical power in a lateraldirection across the stepped waveguides 100, 104.

As illustrated in FIG. 13, the first and second directional backlightsmay be stacked behind the spatial light modulator 48. Each of the firstand second directional backlights may supply output light through thespatial light modulator 48 and through any other directional backlightwhich may be intermediate to the first and second directional backlightsand the spatial light modulator 48.

In the operation of FIGS. 12 and 13, light from light source array 106may pass through the stepped waveguide 104 and subsequently may besubstantially directed through the stepped waveguide 100. For example asshown in FIG. 13, light ray 105 from light source array 106 aftercounter propagating in stepped waveguide 104 may be passed throughstepped waveguide 100, due to the transparent features 10 of the steppedwaveguide 100. The light extraction features 12 of stepped waveguide 100may further be substantially uncoated to achieve further lighttransmission through the stepped waveguide 100. Continuing thedescription of FIG. 13, the directional backlights may be orientedaround the normal to the spatial light modulator 48 so that the opticalwindows provided by the directional backlights may be substantiallyaligned with each other. Additionally, in FIG. 13, the first guidesurfaces of the respective directional backlights may be substantiallycoplanar with one another, as generally illustrated in FIG. 29.

Advantageously such an arrangement can achieve increased displaybrightness as each illuminator array 102, 106 may be arranged to providesubstantially simultaneous illumination of a viewing window 26 orviewing window 44, depending on the display phase. Although similarincreased brightness may be provided by thickening a single illuminatorallowing larger sources to be used, there may be an advantage toemploying more numerous smaller sources. The greater number of smallersources may allow for increased uniformity and improved thermalcharacteristics. Further, the optical output of the two steppedwaveguides can be slightly different to improve output opticaluniformity in the window plane when the two viewing windows aresubstantially overlaid or to provide wider vertical viewing angles. Forexample, losses such as reflection losses arising from transmissionthrough stepped waveguide 100 can be compensated by increasing therelative output luminance of illuminator 106 compared to illuminator102.

Additionally, in the embodiment of FIGS. 12 and 13 the thicker sides 4of the guides are arranged together, as are the LEDs, thus resulting ina thick combined structure with LED mechanical interference issues, forexample increasing package size and total display thickness.

In one illustrative embodiment, the individual directional backlightsmay each have a maximum thickness of 2 mm, and may be placed in a stackincluding Fresnel lens 62 with a combined thickness of for example 5 mm,positioned with a separation 67 to the spatial light modulator 48 anddiffuser 68 of 1 mm or less. Alternatively the separation 67 can beincreased to greater thicknesses to reduce the appearance of Moirépatterning between the repetitive structures of the Fresnel lens 62,backlights 100, 104 and spatial light modulator 48.

FIG. 14 is a schematic diagram illustrating stacked directionalbacklights of a directional display device which includes two steppedwaveguides arranged in series and FIG. 15 is a schematic diagramillustrating in side view a directional display device incorporating thestacked directional backlights of FIG. 14 arranged to provide at leastfirst and second viewing windows. This embodiment is similar to that ofFIGS. 12 and 13 except for the following modifications. As illustratedin FIGS. 14 and 15, the directional backlights may be arranged ininverted orientations around the normal to the spatial light modulator48 with the input end 2 of each directional backlight on the same sideas the reflective end 4 of the other directional backlight. In FIGS. 14and 15, the directional backlights 100 and 104 may have reflective ends4 and input ends 2. In the embodiment of FIGS. 14 and 15, thedirectional backlight 100 may be oriented such that the reflective end 4may be on the same side as the input end 2 of the directional backlight104.

As shown in FIG. 14, a first directional backlight may include thestepped waveguide 100 and the light source array 102 and a seconddirectional backlight may include the stepped waveguide 104 and thelight source illuminator array 106. The first and second directionalbacklight may be stacked behind a spatial light modulator 48. Further asillustrated in FIG. 14, the first and second directional backlights mayinclude a reflective surface. In FIG. 14, the reflective surface is onthe curved end of the first and second directional backlights. In oneembodiment, the reflective surface or reflective end 4 of either one orboth of the stepped waveguides 100, 104 may have positive optical powerin a lateral direction across the stepped waveguides 100, 104.

As illustrated in FIG. 14, the first and second directional backlightsmay be stacked behind the spatial light modulator. Each of the first andsecond directional backlights may supply output light through thespatial light modulator and through any other directional backlightwhich may be intermediate to the first and second directional backlightsand the spatial light modulator.

Continuing the description of FIG. 14, the directional backlights may beoriented around the normal to the spatial light modulator so that theoptical windows provided by the directional backlights may besubstantially aligned with each other. Additionally, in FIG. 14, thefirst guide surfaces of the respective directional backlights may besubstantially coplanar with one another, as generally illustrated inFIG. 29.

Further, FIG. 15 shows the stack in side view in which light ray 105propagates through the stepped waveguide 100 and the stepped waveguidesmay be arranged inverted with respect to each other. Advantageously thisembodiment may provide physically separated LED arrays 102, 106. Theembodiment of FIG. 15 may achieve improved thermal control as thethermal management of the LED arrays 102, 106 may be physicallyseparated. Further, better vertical angular uniformity can be achievedthrough approximate symmetry of output cone directions when the lightextraction features are uncoated. Since most to substantially all lighttravels back from the thick end 4 to thin end 2 and may be extractedwhen the light is incident on a light extraction feature 12, the lightthat makes it back to the thin side 2 without encountering extractionmay be lost to the system. The ratio of height of the thin side 2 tothick side 4 is a measure of an efficiency factor. By way of comparison,using a single stepped waveguide and doubling the thin end to enabletwice the source emission can only be as efficient if the side 4thickness is increased accordingly. The present embodiment may provideapproximately twice the light with a much smaller overall thicknessincrease. Further, advantageously the horizontally aligned lightextraction features 12 may use reflection as a means of extraction. Anyangular variation in reflection such as that seen with total internalreflection (TIR) may introduce significant vertical angular variation inillumination. Inverse stacking may provide vertical symmetry, which mayresult in a more uniform intensity in the vertical viewing window.

FIG. 16 is a schematic diagram illustrating stacked directionalbacklights of a directional display device which includes three steppedwaveguides arranged in series to provide respective red, green and blueillumination directions for illumination of a transmissive spatial lightmodulator and FIG. 17 is a schematic diagram illustrating in side view adirectional display device incorporating the stacked directionalbacklights of FIG. 16. The directional backlights may include at least astepped waveguide and a light source illuminator array. This embodimentis similar to that of FIGS. 12 and 13 except for the followingmodifications.

As shown in FIG. 16, a first directional backlight may include thestepped waveguide 108 and the light source array 110, a seconddirectional backlight may include the stepped waveguide 112 and thelight source illuminator array 114, and a third directional backlightwhich may include the stepped waveguide 116 and the light sourceilluminator array 118. In one example, at least the first, second, andthird directional backlights may be stacked behind a spatial lightmodulator 48. Further as illustrated in FIG. 16, the first, second, andthird directional backlights may include a reflective surface. In FIG.16, the reflective surface is on the curved end of the first, second,and third directional backlights. In one embodiment, the reflectivesurface or reflective end 4 of either one or any combination thereof ofthe stepped waveguides 108, 112, 116 may have positive optical power ina lateral direction across the stepped waveguides 108, 112, 116.

As illustrated in FIG. 16, the first, second, and third directionalbacklights may be stacked behind the spatial light modulator 48. Each ofthe first and second directional backlights may supply output lightthrough the spatial light modulator 48 and through any other directionalbacklight which may be intermediate to the first and second directionalbacklights and the spatial light modulator.

Continuing the description of FIG. 16, the directional backlights may beoriented around the normal to the spatial light modulator 48 so that theoptical windows provided by the directional backlights may besubstantially aligned with each other. Additionally, in FIG. 16, thefirst guide surfaces of the respective directional backlights may besubstantially coplanar with one another, as generally illustrated inFIG. 29.

In one embodiment, with respect to each of the directional backlights,an array of light sources may be located at different input positionsacross the input end of the respective waveguide.

In another embodiment, the directional backlights may be oriented aroundthe approximate normal to the spatial light modulator so that theoptical windows provided by the directional backlights may beapproximately aligned with each other and the array of light sources inrespect of each directional backlight may be arranged to output light ofa different color.

As shown in FIG. 17, a transmissive SLM 48 may be, in turn, illuminatedby a stepped waveguide 108 illuminated by a red LED light source array110; a second stepped waveguide 112 may be illuminated by a green LEDlight source array 114 and a third stepped waveguide 116 may beilluminated by a blue LED light source array 118. Each viewing windowmay be provided by a summation of the light from the respective LEDs inthe arrays 110, 114, 118. Blue ray 117 and green ray 115 may passthrough at least one stepped waveguide of the stack because of theadvantageous transparency properties of the stepped waveguide structure.As shown in FIGS. 14 and 15, the stepped waveguide 112 may be invertedto reduce the mechanical size and improve the thermal management of therespective LED light source array 114. In further embodiments, two ormore stepped waveguide units may be used. For example a first steppedwaveguide may include a green light source array while a second steppedwaveguide may include a red and blue light source array. Advantageouslysuch an embodiment can achieve compensation for the reduced luminousemittance of green inorganic LEDs.

Advantageously, separate color LEDs can be provided compared to thewhite LEDs typically used in other embodiments. Separate color LEDs mayachieve a higher spectral gamut and may operate with high efficiency. Byway of comparison, if the separate red, green and blue LEDs werecombined into a single illumination array for a single steppedwaveguide, the total display luminance that can be achieved may bereduced due to the limited size of the input aperture on the narrow side2 of the respective stepped waveguide.

FIG. 18 is a schematic diagram in top view, a detail of one embodimentof spatial light modulator of FIG. 16 arranged to achieve efficientillumination of red, green, and blue pixels of the respective spatiallight modulator. Further, FIG. 18 shows an embodiment in which thedirectional red, green and blue illumination of the respective steppedwaveguides 108, 112, 116 can be used to illuminate a monochromatic SLM49. A microlens array 120 is provided in approximate alignment with redpixels 122, green pixels 124 and blue pixels 126. Red stepped waveguide108 may provide a substantially collimated wavefront with direction 129and which may be focused into a light cone 128 incident onto red datapixels 122; green stepped waveguide 112 may provide a substantiallycollimated wavefront with direction 127 which may be focused into alight cone 130 incident onto green data pixels 124; and blue steppedwaveguide 116 may provide a substantially collimated wavefront withdirection 131 which may be focused into a light cone 132 incident ontoblue data pixels 126. A final diffuser 134 may be provided to enablesome color mixing and redistribution of light output cones to achieve awider panel viewing angle. Alternatively, the red, green and blue LEDscan be arranged in series at the input aperture on the narrow side 2 ofa single stepped waveguide to provide a more compact arrangement.Advantageously this embodiment may remove the requirement for individualcolor filters in the SLM and so can achieve higher efficiency.

FIG. 19 is a schematic diagram of stacked directional backlights of adirectional display device that includes two stepped waveguides arrangedin series to provide landscape and portrait autostereoscopic viewing andFIG. 20A is a schematic diagram in side view of a directional displaydevice incorporating the stacked directional backlights of FIG. 19.Further, FIG. 19 shows an embodiment schematically and FIG. 20A shows inside view the embodiment including a crossed stack of steppedwaveguides, each of which may provide a substantially one dimensionalarray of viewing windows. This embodiment is similar to that of FIGS. 12and 13 except for the following modifications.

The first directional backlight of FIGS. 19 and 20A may include astepped waveguide 100 and a light source illuminator array 102 and thesecond directional backlight may include a stepped waveguide 104 and alight source illuminator array 106. As illustrated in FIGS. 19 and 20A,the first and second directional backlights are approximately orientedaround the normal to the spatial light modulator 48 so that the sets ofoptical windows 26 and 44 provided by the first and second directionalbacklights may extend at an angle relative to each other in a range from85 to 95 degrees. The limits of this range are approximate.

As shown in FIG. 19, a first directional backlight may include thestepped waveguide 100 and the light source array 102 and a seconddirectional backlight may include the stepped waveguide 104 and thelight source illuminator array 106. The first and second directionalbacklight may be stacked behind a spatial light modulator. Further asillustrated in FIG. 19, the first and second directional backlights mayinclude a reflective surface. In FIG. 19, the reflective surface is onthe curved end of the first and second directional backlights. In oneembodiment, the reflective surface or reflective end of either one orboth of the stepped waveguides 100, 104 may have positive optical powerin a lateral direction across the stepped waveguides 100, 104.

As illustrated in FIG. 19, the first and second directional backlightsmay be stacked behind a spatial light modulator. Each of the first andsecond directional backlights may supply output light through thespatial light modulator and through any other directional backlightwhich may be intermediate to the first and second directional backlightsand the spatial light modulator.

Continuing the description of FIG. 19, the directional backlights may beoriented around the normal to the spatial light modulator so that theoptical windows provided by the directional backlights may besubstantially aligned with each other. Additionally, in FIG. 19, thefirst waveguide surfaces of the respective directional backlights may besubstantially coplanar with one another, as generally illustrated inFIG. 29. Additionally the optical axes 321, 323 of respective stackeddirectional backlights 100, 104 are arranged to be substantiallyorthogonal.

As shown in FIG. 20A, stepped waveguide 100 may be arranged to transmitlight rays 119 from the stepped waveguide 104 without substantiallyaltering the directionality of the light rays. Thus, a first set ofviewing windows 26 can be provided by stepped waveguide 100 while asecond set of viewing windows 44 can be provided by the steppedwaveguide 104 that may be inclined to, for example approximatelyorthogonal to, the viewing windows 26. The Fresnel lens 62 may haveapproximately rotational symmetry, while a weak rotationally symmetricdiffuser 69 may be provided to improve viewing window uniformity.

Advantageously the arrangement of FIGS. 19 and 20A may provide aswitchable landscape-portrait mode of operation. When illuminator 102 isswitched on, a tracked landscape autostereoscopic mode can be produced.In one example, if an observer rotates a handset (not illustrated inFIGS. 19 and 20A), the viewing orientation may be sensed as havingchanged and the illuminator 102 may be switched off and illuminator 106may be switched on. Further, the image data may be rotated on the panel.In this manner, a full resolution observer tracked autostereoscopicdisplay may be provided in both panel orientations.

[Adapt to use wording consistent with claims 11 and 12]

FIG. 20B is a schematic diagram in side view a stacked imagingdirectional backlight apparatus including two stepped waveguidesarranged in series with a spatial light modulator. As illustrated inFIG. 20B, a first directional backlight may include at least a steppedwaveguide 100 and a second directional backlight may include at least astepped waveguide 104. Similar to the embodiment of FIGS. 14 and 15, thestepped waveguides 100 and 104 may be arranged in inverted orientationsaround the normal to the spatial light modulator with the input end ofeach stepped waveguide on the same side as the reflective end of theother stepped waveguide. Stated differently, the stepped waveguide 100may be oriented such that the reflective end may be on the same side asthe input end of the stepped waveguide 104. Additionally, in FIG. 20B,the first guide surfaces of the respective directional backlights may besubstantially coplanar with one another, as generally illustrated inFIG. 29. Further as illustrated in FIG. 20B, the facing waveguidesurfaces of the directional backlights may be arranged in invertedorientations and may extend in a generally parallel direction.

Further, FIG. 20B shows an embodiment arranged to reduce the packagethickness of the stack. Spacer elements 334, 336 may be arranged betweenthe spatial light modulator 48 and the stepped waveguide 100, andbetween adjacent stepped waveguides 100, 104 respectively. The spacerelements 334, 336 may be, but are not limited to, spacer balls, adhesivespacer balls, may be photospacers or may be linear in form, and soforth. Further, the spacer elements may be formed with the steppedwaveguide during molding. Advantageously such spacer elements mayachieve an air gap between the structures while minimizing the gap andmaintaining flat surfaces. The size of the features may be small enoughto have reduced visibility and scattering during operation, and in oneexample may be spheres or cylinders with diameters of approximately 25micrometers.

FIG. 20C is a schematic diagram in side view and further illustratesstacked directional backlights of a directional display device whichincludes two stepped waveguides arranged in series with a spatial lightmodulator. Further, FIG. 20C shows a stepped waveguide stack including alow refractive index coating 322 between the stepped waveguide 100 and aspatial light modulator 48 which may include a liquid crystal displayincluding polarizers 324, 332, substrates 326, 330 and switchable liquidcrystal layer 328. A limited cone angle 316 may be provided within thestepped waveguide 100 so that the critical angle that can be provided atthe surface of the stepped waveguide 100 at the side 6 is increased. Inan illustrative example, a total cone angle of approximately 26° may beguided within a stepped waveguide with the critical angle at the surfaceinterface of side 6 of less than approximately 77°. Such an interfacemay, for example, be provided by a bulk refractive index of the steppedwaveguide 1 of approximately 1.5, with a low index coating layer 322 ofapproximate refractive index 1.4, providing a critical angle ofapproximately 71°. For example, material of layer 322 may include, butis not limited to, a silicone, an aerogel, a fluorinated polymer, and soforth. Advantageously such an arrangement may provide a reducedthickness device that may be mechanically stabilized by the liquidcrystal panel. Further light losses due to Fresnel reflections may beminimized for the output light from the extraction features 12 (notshown in FIG. 20C), thus reducing cross talk in the display system.

Further, the side 6 of stepped waveguide 104 may contact the cusps oflight extraction features 12 in side 8 of stepped waveguide 100 toprovide a low package thickness with low coupling between the respectivestepped waveguides. Advantageously these embodiments may provide lowtotal package thicknesses.

FIG. 21A is a schematic diagram illustrating tiled directionalbacklights of a directional display device which includes two steppedwaveguides arranged to achieve increased illumination area, and FIG. 21Bis a schematic diagram illustrating in side view, a directional displaydevice incorporating the tiled directional backlights of FIG. 21A.

As shown in FIGS. 21A and 21B, the directional backlights may includethe stepped waveguides 100, 104, and light source illuminator arrays 102and 106 respectively. As shown in FIG. 21B, the directional backlightsmay be tiled behind the display 48, which in one example, may be aspatial light modulator. Additionally as illustrated in FIG. 21B, thedirectional backlights may be tiled behind a diffuser 68 and a Fresnellens 62 and may supply output light through different regions of the SLM48. The diffuser 68 and the Fresnel lens may be omitted, usedindividually, or in combination in the tiled imaging directionalbacklight apparatus of FIG. 21B. Continuing the description of FIGS. 21Aand 21B, the directional backlights may be tiled in the direction of theoptical axis of the stepped waveguides 100 and 104 so as to supplyoutput light through different regions of the SLM 48. The steppedwaveguide 100 may have a reflective end and the reflective end of thestepped waveguide 100 may overlap the stepped waveguide 104. Thereflective end of the directional backlight may have positive opticalpower in the direction across the waveguide.

Thus the optical axes 321, 323 of the directional backlights 100, 104are aligned and parallel and the first and second directional backlights100, 104 may be tiled in a direction perpendicular to the lateraldirection. Stated differently, the first and second directionalbacklights 100, 104 may be tiled in the direction of the optical axes321, 323 of the waveguides 100, 104.

Further, a tiled imaging directional backlight embodiment is shownschematically in FIG. 21A and in side view in FIG. 21B in which thestepped waveguides 100, 104 are provided with curved end sections andoffset to achieve differential top and bottom panel illumination. Thisconfiguration may achieve higher brightness at a given thickness over asingle stepped waveguide as well as allowing independent localillumination for improved contrast and efficiency. The steppedwaveguides 100, 104 may be arranged with side 6 of stepped waveguide 104inclined to the display 48 for example as shown, or may be parallel.Advantageously inclined elements may provide a lower total thickness. Aswill be described with reference to FIG. 32, such an arrangement canfurther provide improved cross talk and brightness in scanned timesequential autostereoscopic displays. As will be described withreference to FIG. 28C, the sides of the respective optical valves mayinclude Fresnel reflectors to reduce the surface sag, advantageouslyreducing the visibility of the seam between the respective steppedwaveguides 100, 104.

FIG. 22 is a schematic diagram illustrating an array of tileddirectional backlights including rows of stepped waveguides. Further,FIG. 22 shows schematically an array 201 of stepped waveguides 101including rows 203, 205, 207 of stepped waveguides 101. Similar to thedirectional backlights of FIGS. 21A and 21B, the directional backlightsof FIG. 22 may include stepped waveguides. The stepped waveguides 101 ofFIG. 22 may be tiled in both the lateral direction and in a directionperpendicular to the lateral direction, so as to supply output lightthrough different regions of the SLM 48.

First and second rows are offset by half the length of a steppedwaveguide thus provide joins in different locations. When combined witha diffuser 68 separated from the array 201, as shown in FIG. 21B, theoutput of the respective stepped waveguides may be overlapped to reducethe visibility of luminance differences between the respective steppedwaveguides, advantageously increasing display uniformity over a largearea. A first tiled stepped waveguide array such as that shown in FIG.22 may also be stacked with a second tiled stepped waveguide array. Thejoins between the respective first and second tiled arrays can be offsetso as to advantageously reduce the intensity variation between therespective tiles of the waveguides.

FIG. 23 is a schematic diagram illustrating tiled directional backlightsof a directional display device which includes two stepped waveguidesarranged to achieve increased illumination area, and FIG. 24 is aschematic diagram illustrating in side view, directional display deviceincorporating the tiled directional backlights of FIG. 23. Further, FIG.23 shows schematically and FIG. 24 shows in side view a furtherarrangement of the tiled stepped waveguides. The arrangement is similarto that of FIGS. 21A and 21B but with the following modifications. Thefirst and second directional backlights 100, 104 may be tiled in adirection perpendicular to the lateral direction. However, steppedwaveguide 100 has a further parallel input section planar waveguide 140incorporated at the input surface such that light from light sourceilluminator array 102 is directed towards the valve section withoutsubstantial loss prior to expanding in the wedge section as for astandard stepped waveguide. Light from the stepped waveguide 104 thenpasses through the input section planar waveguide 140 withoutsubstantially modifying directionality.

FIG. 25 is a schematic diagram illustrating in side view tileddirectional backlights of a directional display device which includestwo stepped waveguides arranged to achieve increased display area, andFIG. 26 is a schematic diagram illustrating in side view tileddirectional backlights of a directional display device which includestwo stepped waveguides arranged to achieve increased display area.Further, FIG. 25 shows a side view of an arrangement similar to that ofFIG. 24 but in which the order of the components is reversed.Advantageously such an arrangement may reduce light loss due to Fresnelreflections of light transmitted through the section 104 in FIG. 24.Additionally, FIG. 26 shows a further embodiment of an arrangementsimilar to that of FIG. 24 but wherein an additional backlight includingstepped waveguide 103 and light source array 105 may advantageouslyincrease display size and brightness, together with cross talkreduction.

FIG. 27 is a schematic diagram illustrating tiled directional backlightsof a directional display device which includes two stepped waveguidesarranged to achieve increased illumination area, and FIG. 28A is aschematic diagram illustrating in side view the tiled imagingdirectional backlights. The arrangement is similar to that of FIGS. 23and 24 but with the following modifications. Further, FIG. 27 showsschematically and FIG. 28A shows in side view an inverted arrangement ofstepped waveguides 100, 104 incorporating parallel input section planarwaveguides 140, 142 respectively. Advantageously the optical propertiesof the two stepped waveguides may be matched to provide improved displayuniformity.

Advantageously the arrangements of FIGS. 23 to 28A may achieve areduction in Moiré beating between the light extraction features of thefirst stepped waveguide 100 and the second stepped waveguide 104, whilesubstantially maintaining brightness of the output. Further the LEDlight source illuminator arrays 102, 106 are substantially coplanar socan be conveniently arranged on a single heat sink and electricalconnection apparatus.

FIG. 28B is a schematic diagram illustrating in side view tileddirectional backlights of a directional display device which includestwo stepped waveguides arranged to achieve increased display area. Lightextraction side 143 (including features 10, 12) of at least the upperstepped waveguide may be provided with a reflective coating such as ametallized layer. Light extraction side 145 (including features 10, 12)of the lower stepped waveguide may also be provided with a reflectivecoating. An overlap region 147 may be provided between the upper andlower extraction regions. Advantageously such an arrangement may achievea substantially continuous output illumination uniformity. Region 147may achieve uniform output over a wide cone angle while achieving adesired separation between upper and lower stepped waveguides.

FIG. 28C shows a further embodiment of a stepped waveguide for stackingin tiling. Side 4 includes a Fresnel lens structure 149 arranged toreflect and focus light from the illuminator array 15. Advantageouslysuch an arrangement can achieve a reduction in the size of the endreflector, reducing package size and visibility of seams in stacking andtilting arrangements.

FIG. 29 is a schematic diagram illustrating an array of tileddirectional backlights of a directional display device. Further, FIG. 29shows schematically another embodiment in which multiple valves ordirectional backlights are arranged tiled in both the lateral directionand the direction perpendicular thereto. Similar to the directionalbacklights of FIGS. 21A and 21B, the directional backlights of FIG. 29may include stepped waveguides. The stepped waveguides of FIG. 29 may betiled in both the lateral direction and the direction perpendicularthereto.

As shown in FIG. 29, the multiple stepped waveguides may be tiled in anarray 150 and aligned to display 48 to advantageously achieve a largearea illumination of the observer 45. The display 48 may provide a firstviewing window 44 and a second viewing window 26. The first viewingwindow 44 may provide an image to the right eye of the observer 45 andthe second viewing window 26 may provide an image to the left eye of theobserver 45.

FIG. 30 is a schematic diagram illustrating propagation of light in anarray of tiled directional backlights. Further, FIG. 30 showsschematically a stepped waveguide in which the side 4 includes first andsecond reflectors 320, 322, respectively. Similar to the directionalbacklights of FIGS. 21A and 21B, the directional backlights of FIG. 30may include stepped waveguides. The stepped waveguides of FIG. 30 may betiled in the lateral direction so as to supply output light throughdifferent regions of the SLM 48. Stated differently, the waveguides maybe tiled in a direction substantially perpendicular to the optical axisof the stepped waveguides 101. Further, the directional backlights ofFIG. 30 may include light emitting element arrays 326, 324. The lightemitting element array 326 may include a light emitting element 326 andthe light emitting element array 324 may include a light emittingelement 325.

Such an arrangement of stepped waveguides may be fabricated as a singlemolded piece, may be assembled by attaching adjacent stepped waveguides.Additionally, the stepped waveguides may be assembled by attachingcurved end segments to the end of a structure including an input side 2,a side 6 and continuous linear light extraction features 10, 12 arrangedas described herein, but not illustrated in FIG. 30. The steppedwaveguides of the directional backlights may also be formed from acommon piece of material. Light emitting element arrays 326, 324 may bearranged so that light may propagate onto respective reflectors 322,320. Light may also propagate from array 324 to reflector 322 and viceversa, to produce viewing lobes for the particular reflector. The arrays326, 324 may be arranged so that respective light emitting elements 327,325 are arranged to be directed by respective reflectors 322, 320 to theviewing window 26.

Continuing the discussion, the output pupillation to combine light raysat viewing window 26 may be achieved by a combination of the reflectors320, 322 and light extraction features 12. Furthermore, FIG. 31 is aschematic diagram illustrating details of light propagation in an arrayof stepped waveguides and an output Fresnel lens. As shown in FIG. 31 aFresnel lens 62 may further be included. In FIG. 31, the Fresnel lens 62is shown for illustrative purposes as being at the exit of the inputside 2. However, the Fresnel lens 62 may be substantially parallel tothe output surface 6, and the output light may not pass through side 2so that light extracted by features 12 is incident thereon. Light rays335 from array 324 are shown with open arrows while light rays 337 fromarray 326 are shown with closed arrows.

Advantageously the arrangement of FIG. 31 may distribute optical powerbetween the reflectors 320, 322 and the Fresnel lens 62. The Fresnellens 62 area may be substantially the same size as the total steppedwaveguide array area. In further embodiments, the single Fresnel lens 62may be replaced by an array of Fresnel lenses each arranged with atleast one stepped waveguide of the array of stepped waveguides. Inoperation, light rays 335, 337 may be directed by reflectors 320, 322with respective centers of curvature 330, 333, with reflected lightcones that may be convergent, divergent or parallel; in the exampleillustrated in FIG. 31, divergent light beams are shown. On exiting thestepped waveguide by extraction at features 12, this light is incidentonto the Fresnel lens 62 where it is imaged towards the observer. Giventhe divergence of the output beams in this embodiment, the Fresnel lensmay have a virtual object point 328 defined by virtual light rays 329.Advantageously divergent beams may reduce the size of non-illuminatedregions in stepped waveguides for off-axis viewing points.

Light cone 336 illustrates a region of illumination for light rays 335falling on reflector 320 that forms a folded optical path to illuminatea region 338 that is not within the logical light guide section forreflector 320. The logical light guide section being the region of thestepped waveguide that is substantially directly under the reflector320. Thus light is not reflected by reflectors 322, 320 to be entirelywithin respective light guide sections, but may propagate betweenadjacent sections of the stepped waveguide to provide illumination ofthe viewing window 26.

Advantageously the output of the array of stepped waveguides which mayinclude an array of reflectors 320, 322, may achieve substantiallyuniform illumination to the viewing window 26 over approximately thewhole of the display area while maximizing illuminated display area atthe limits of lateral viewing freedom.

In field sequential autostereoscopic displays, separated top and bottomillumination can significantly improve illumination duty cycle ashalf-height regions of a line-by-line updated LCD provides settledimagery for a significant proportion of the overall frame time. Theoperation of an offset stacked illuminator within an autostereoscopicdisplay system is illustrated schematically in FIG. 32. Further, FIG. 32is a schematic diagram illustrating scanned addressing of anautostereoscopic display in cooperation with an array of steppedwaveguides. FIG. 32 includes a viewer 45, and a SLM 48, in which theimages on the SLM 48 sequentially vary in the direction 152.

In a first time slot 154, the SLM 48 is showing right eye image 162 overmost of the SLM height except for the top portion which includes aswitching region 164. Thus observer at time slot 154 has the right eyeviewing window illuminated by just the bottom stepped waveguide 104. Inthe next time slot 155 the SLM shows a mixture of right image 162, mixedimage 164 and left image 166. In time slot 156, the left image appearsat the top of the display with mixed region at the bottom so thatstepped waveguide 100 illuminates the left eye viewing window andstepped waveguide 104 is un-illuminated. In time slot 157 both top andbottom of the SLM show mixed images so both stepped waveguides areun-illuminated. In time slot 158 the bottom valve illuminates the leftviewing window. In time slots 159 and 161 neither stepped waveguide isilluminated, and in time slot 160 the top stepped waveguide 100 isilluminated for the right eye viewing window. Thus, through the timingsequence each eye sees the left and right eye from the top and bottom ofthe array of stepped waveguides.

FIG. 33 is a schematic diagram illustrating in side view, scannedaddressing of an autostereoscopic directional display deviceincorporating an array of tiled directional backlights. In FIG. 33, timeslot 160 is illustrated in side view so that light source illuminatorarray 102 is arranged to provide right eye illumination through steppedwaveguide 100 while light source illuminator array 106 isun-illuminated. The transparency of the stepped waveguides 100 and 104achieves a substantially uniform output intensity over the integratedillumination from the display for left and right eye images. As thedisplays are not illuminated in the switching regions, the cross talk ofthe display is advantageously reduced, and the brightness is improved asthe display may be illuminated for a longer total time slot than forsingle stepped waveguide illumination scheme.

FIG. 34A is a schematic diagram illustrating in front view an array oftiled directional backlights of a directional display device arranged toprovide an increased illumination area. FIG. 34A shows in front view thearray of tiled directional backlights.

A first directional backlight includes a stepped waveguide 181 and anarray of light sources 181 and a second directional backlight includes astepped waveguide 182 and an array of light sources 183. The directionalbacklights are tiled behind the spatial light modulator in a directionperpendicular to the lateral direction. As a result they supply outputlight through different regions of the spatial light modulator. Thereflective ends of each stepped waveguide are coplanar at a boundary179. The stepped waveguides may include light extraction features 12that are curved to provide a positive optical power in the lateraldirection. This allows the boundary 179 forming the reflective ends ofeach stepped waveguide to be flat, and thus permitting the waveguides180, 182 to be butted with a minimal gap between the light outputsection of the two units. In this context, the boundary 179 being “flat”means that it is sufficiently flat to provide consistent opticalproperties thereacross to allow proper functioning, and there may besome roughness at a small scale.

Such a stepped waveguide may achieve a magnification of viewing windowsthat varies along the length of the stepped waveguide. Preferably afurther imaging element such as Fresnel lens of FIG. 28C may be providedto avoid the variation of magnification with length.

To make it reflective the boundary 179 may be a substantially or fullysilvered surface as shown in FIG. 34B. FIG. 34B is a schematic diagramillustrating in side view, an array of directional backlights to providean increased illumination area. The stepped waveguides may operatesubstantially independently but may include further stepped waveguidearrays to the rear to provide additional functionality as describedpreviously. The stepped waveguide array as shown is not monolithic orformed in a single layer structure, as the mirror at the boundary 179may provide a break in the layer.

FIG. 34C is a schematic diagram illustrating in side view an array ofbacklights to provide an increased illumination area, similar to that ofFIG. 34A. FIG. 34C shows an embodiment in which the boundary 179 may beformed from a semi-silvered mirror, such as provided by a small gapbetween the stepped waveguides 180, 182, or by a semi-transparent metallayer for example. The light from the array of light sources 183 of thedirectional backlight also including the waveguide 182 is split into alight ray 186 that is reflected from the boundary 179 forming areflective end of the waveguide 182 and into a light ray 185 that passesthrough the boundary. Thus, the light ray 186 is output as output lightthrough the waveguide 182 and the light ray 185 is output as outputlight through the waveguide 180. The light from the array of lightsources 181 of the directional backlight also including the waveguide180 is split in a similar manner. Thus, light rays from source array 183may propagate within stepped waveguides 180 and 182, thus mixing withlight from light source array 181 increasing total brightness andproviding mixing between the two arrays of light sources 181, 183.Furthermore, the mixing of light between the two light source arrays mayadvantageously compensate for differences in color and brightnessbetween the two arrays of light sources 181, 183, increasing uniformity.

FIG. 34D is a schematic diagram illustrating in front view a directionalbacklight including linear light extraction features and a planardiffractive reflector arranged to provide focusing of incident light.Further, FIG. 34D shows a stepped waveguide 302 including a diffractivereflector 300 and linear light extraction features 12. Light emittingelements in the illuminator array 15 may illuminate the reflector 300and are focused, for example, to parallel light for subsequent imagingof viewing windows by a Fresnel lens (not shown in FIG. 34D). Thediffractive reflector 300 may include a holographically recordeddiffraction pattern that may achieve a focusing function and may forexample be a volume hologram. Moreover, the reflector 300 may includestacks of red, green and blue reflection diffractive elements or may beformed by multiple recordings in a single layer. The spectral efficiencyof the reflector 300 may be tuned to the output wavelengths of the lightemitting elements of the illuminator array 15. The light emittingelements may include narrow band emission to provide high efficiency ofreflection. The reflector may be recorded to provide low aberrationsover a range of illumination angles including the length of theilluminator array 15, and may include multiple diffractive structures toachieve high efficiency over the respective range of illuminationangles.

Advantageously the reflector 300 may be a planar structure that can beattached to a planar surface of the stepped waveguide. Thus the steppedwaveguide fabrication may have reduced cost and complexity.Additionally, the plane surface can be arranged in tiled arrays as willbe described below. Further, the efficiency of the structure may beoptimized by matching to the illumination wavelengths and angles.Moreover, the attachment of the reflector 300 may not require anevaporative coating, and so cost can be reduced.

FIG. 34E is a schematic diagram illustrating in front view imaging by adirectional backlight including curved light extraction features and aplanar diffractive reflector arranged to provide focusing of incidentlight. Further, FIG. 34E shows a further embodiment including a steppedwaveguide 306 in which optical power is shared between a diffractivereflector 304 and curved light extraction features 12, to provide aviewing window 26, for example without using an additional Fresnel lens62. Advantageously such an embodiment can provide reduced aberrations,reduced Moire, lower device thickness and lower cost.

FIG. 34F is a schematic diagram illustrating in side view an array oftiled directional backlights of a directional display deviceillustrating light propagation for light output in a tiled array ofstepped waveguides including a holographic reflector. FIG. 34G shows infront view the same array of tiled directional backlights. The array oftiled directional backlights is similar to that of FIG. 34A except forthe following modifications.

A first directional backlight includes a stepped waveguide 302 and anarray of light sources 15 and a second directional backlight includes astepped waveguide 310 and an array of light sources 15. The directionalbacklights are tiled behind the spatial light modulator in a directionperpendicular to the lateral direction. As a result they supply outputlight through different regions of the spatial light modulator. Thereflective ends 300, 308 of the respective waveguides 302, 320 arecoplanar and flat, as described above.

FIG. 34F shows in side view propagation of light rays in a tiled arrayof stepped waveguides 302, 310 in which the reflectors 300, 308 may bearranged in close proximity. The reflective ends 300, 308 may bediffractive reflectors having positive optical power in a lateraldirection. Thus the reflective ends 300, 308 may be arranged to reflectlight rays 312 propagating within the stepped waveguide but also totransmit off-axis light rays 314 due to the angular selective propertiesof the diffractive reflectors 300, 308. Advantageously the visibility ofthe join between the stepped waveguides 302, 310 may be reduced.Additionally, the light cone with the stepped waveguides 302, 310 may bereduced such that off-axis light does not propagate, thus increasing theoverall reflector efficiency by reducing incident cone angles.

The diffractive reflectors may take any of the forms described abovewith reference to FIG. 34D. The diffractive reflectors and steppedwaveguides may be attached to each other by a suitable index matchingadhesive. Alternatively the diffractive reflectors may be formed as asingle element on recording. In yet another alternative, the reflectorsmay include additional absorbing layers to substantially prevent lightfrom stepped waveguide 302 propagating into stepped waveguide 310.

FIGS. 35 to 38 illustrate respective arrays of tiled directionalbacklights similar to that of FIG. 30 in that they are tiled in thelateral direction and include waveguides formed from a common piece ofmaterial, but with further modifications as follows.

FIG. 35 is a schematic diagram illustrating in front view an array oftiled directional backlights to provide an increased illumination area.The directional backlights include respective stepped waveguides, 187,188, 189, separated by effective boundaries 197 that may besubstantially transparent to light from illuminator arrays 15. In FIG.35, each of the directional backlights may include a stepped waveguideand a light source illuminator array. Light rays 195 from light sourceilluminator array 15 associated with stepped waveguide 188 may be guidedthrough the boundary 197 at the cusps of extraction features 12 and somay be directed by first stepped waveguide 188 and second steppedwaveguide 187. The light ray 195 is shown schematically as reflectingoff of the reflective surface 4 and exiting the stepped waveguide 187 atan extraction feature 12. In one embodiment, the light extractionfeatures 12 of each directional backlight may have positive opticalpower in a lateral direction across the stepped waveguide, such that thedeflection of an incident ray varies with offset of the ray from theoptical axis 321 of the respective directional backlight.

Advantageously, such an arrangement can reduce the numerical aperture ofthe curved extraction features 12, thus improving aberrationperformance, reducing cross talk and increasing the range for observertracking without noticeable display flicker. Further, the display areaand brightness can be increased and cross talk reduced using thetemporal scanning methods shown in FIG. 32 for example. In this case thepanel 48 addressing may be side-to-side rather than top-to-bottom.

FIG. 36 is a schematic diagram illustrating in front view an array oftiled directional backlights to provide an increased illumination area.Further, FIG. 36 shows a further embodiment in which a Fresnel lens 178may be incorporated over the array of tiled directional backlights, sothat the optical power may be distributed between the curved extractionfeatures 12 and the Fresnel lens 178. In FIG. 36, each of thedirectional backlights may include a stepped waveguide and a lightsource illuminator array. In one embodiment, the light extractionfeatures 12 of each directional backlight may have positive opticalpower in a lateral direction across the stepped waveguide.

A Fresnel lens may alternatively be arranged with individual steppedwaveguides of the array, or may be arranged with groups of steppedwaveguides so that the display includes multiple Fresnel lenses acrossthe area of the display. Advantageously Fresnel lenses may improveaberrations and achieve stepped waveguides with the same curvedextraction feature arrangement, achieving reduced cost for large areaarrays of stepped waveguides, as the stepped waveguides may be formed bythe same molding process.

FIG. 37 is a schematic diagram illustrating in front view an array oftiled directional backlights to provide an increased illumination area.In FIG. 37, each of the directional backlights may include a steppedwaveguide and a light source illuminator array. In one embodiment, thelight extraction features 12 of each directional backlight may havepositive optical power in a lateral direction across the steppedwaveguide. Further, FIG. 37 shows an embodiment in which the separatelight source illuminator arrays 15 may be replaced by a single lightsource illuminator array 190 at the input side of the array of steppedwaveguides. Advantageously such an arrangement can produce an extendedarray of viewing windows, increasing viewing freedom of the display.

FIG. 38 is a schematic diagram illustrating an embodiment in which tileddirectional backlights incorporate light blocking layers at theinterface between separate stepped waveguides. Further, FIG. 38 shows afurther embodiment in which the stepped waveguides 187, 188, 189 mayincorporate light blocking layers 173 at the interface between separatestepped waveguides. Such light blocking layers 185 advantageouslyachieve a reduction in the cone angle of illumination to provide aprivacy mode and to substantially prevent the loss of visibility of edgepositioned stepped waveguides for off-axis viewing of the display ofFIG. 37. In FIG. 38, each of the directional backlights may include astepped waveguide and a light source illuminator array. In oneembodiment, the light extraction features 12 of each directionalbacklight may have positive optical power in a lateral direction acrossthe stepped waveguide.

FIG. 39 is a schematic diagram illustrating in front view an array oftiled directional backlights to provide an increased illumination area.Further, FIG. 39 shows in front view a further embodiment in which tiledstepped waveguide array 191, including stepped waveguides 187, 188, 189,(not shown in FIG. 39), may be approximately aligned with a similartiled stepped waveguide array 193 in a similar manner to that shown inFIGS. 34A-34C for example. Advantageously such an arrangement mayachieve increased display area, and extended viewing freedom whilereducing aberrations in individual stepped waveguides and thusincreasing maximum observer tracking speed without flicker and reducingimage cross talk.

FIG. 40 is a schematic diagram illustrating in side view, the boundarybetween two stepped waveguides of an array of tiled directionalbacklights. FIG. 40 shows in side view the boundary between two endbutted stepped waveguides with a plane boundary, similar to that shownin FIG. 34B. If the light extraction features 196 are uncoated thenlight cones 202, 204 extracted from the stepped waveguides 194, 198 willtypically have different orientations as shown, and thus each part ofthe tiled stepped waveguide array will have a different brightness fromdifferent directions. As shown in FIG. 41, this can be overcome by usingmetallized light extraction features 206, 208 inclined at approximately45 degrees so that cones 202, 204 are directed parallel to each other.FIG. 41 is a schematic diagram illustrating in side view, the boundarybetween two stepped waveguides of an array of directional backlights.

Thus it is possible to provide tiled arrays of tiled directionalbacklights in which the thickest parts of the stepped waveguides, whichmay typically include a metallized surface, may be butted together.However to further increase display size while substantially maintainingdisplay brightness and aberration performance, it may be desirable toprovide tiled and stacked arrays of stepped waveguides at the thin endor light source input end of the respective stepped waveguides.

One embodiment of an overlapping thin end stepped waveguide is shown inside view in FIG. 42. Further, FIG. 42 is a schematic diagramillustrating in side view first and second ends of a stepped waveguide.The thick end of a stepped waveguide 212 may be arranged with lightextraction features 218 and guiding features 219. The reflective end maybe provided by a corner feature including facets 222 and 224, so as toprovide a retroreflection as opposed to a mirror reflection for guidedlight in the xz plane. At the thin end of a stepped waveguide 210extraction features 216 and 218 may be provided as well as a turningfacet 220 and planar input section planar waveguide 214, which may bearranged to direct light from the light source illuminator array 15 intothe guiding section of stepped waveguide 210.

FIG. 43 is a schematic diagram illustrating in side view first andsecond ends of a stepped waveguide assembled in an array of directionalbacklights. As shown in side view in FIGS. 42 and 43, light rays 228guided in stepped waveguide 212 may be reflected at surfaces 222, 224and counter-propagate towards the respective extraction features 218.Light rays 226 from light source illuminator array 15 in steppedwaveguide 210 may be collected in the section planar waveguide 214 anddirected by reflection at turning facet 220, the mirror that may beprovided by metallization on facet 222, into the stepped waveguide 210.Light rays that are not captured by the section planar waveguide 214 maybe collected in light baffle 215. Counter-propagating light rays 230incident on facets 216 may be directed as in the standard steppedwaveguide arrangement. Near to the overlap region, additional lightextraction features may be incorporated and arranged to direct lightonto the facet 232 and thus direct light from the overlap region to theobserver. A vertical diffuser 68 may be further incorporated to providefurther blurring of the overlap region, advantageously increasing outputuniformity. In this manner, an array of tiled waveguides may be producedto achieve large display area, as may be suitable for example for largearea 3DTV applications.

FIG. 44A is a schematic diagram illustrating in side view, a steppedwaveguide suitable for an array of directional backlights. Further, FIG.44A shows in side view a further embodiment, in which the section planarwaveguide 214 may be folded to the rear of the stepped waveguide 234,including an additional reflective facet 236. As shown in FIG. 44B, inalignment the stepped waveguides may provide a similar arrangement tothat of FIG. 43. FIG. 44B is a schematic diagram illustrating in sideview first and second ends of a stepped waveguide assembled in an arrayof directional backlights. Advantageously such structures may be morecompact than that shown in FIG. 43. Further, the section planarwaveguide 214 may be substantially transparent so that stackedstructures can be implemented, for example by positioning in the gap 237between the section planar waveguide 214 and the stepped waveguide 234.

FIG. 45 is a schematic diagram illustrating in side view first andsecond ends of a stepped waveguide including diffractive reflectors.Further, FIG. 45 shows in side view a further embodiment includingdiffractive reflectors 316, 318 on adjacent stepped waveguides. Thereflectors may be formed as described elsewhere, and may be holographicreflectors. Guiding light rays 318, 322 may be reflected by thereflectors 318, 322 while light rays 324 may be transmitted.Advantageously, the appearance of the gap between adjacent valves can bereduced, and may be used to achieve tiling of stepped waveguides over alarge display area; for example for autostereoscopic 3DTV.

FIG. 46 is a schematic diagram illustrating in side view, an array ofdirectional backlights. Further, FIG. 46 shows a further embodiment inwhich an array of directional backlights including various features ofthe previous embodiments are combined into a stepped waveguide array.Thus stepped waveguides 248, 252 are approximately aligned with steppedwaveguides 244, 240 respectively and the two stepped waveguide pairs maybe butted at interface 179 that may have the properties as previouslyoutlined.

Additionally, FIG. 47 is a schematic diagram illustrating in front view,an array of directional backlights. In front view, as shown in FIG. 47,the stepped waveguides may be provided in a large tile suitable forlarge area display with regions of stepped waveguides that may beaddressed independently through light source arrays 252, 240, 244, 248respectively. Overlap regions 256, 258 may have their visibility reducedby means of additional facets 216 and vertical diffusers 68.Advantageously, such a mechanism can be extended to large areas withindividual addressable characteristics to reduce cross talk, increaseviewing freedom, increase brightness and reduce display flicker.

FIG. 48A is a schematic diagram illustrating in side view, a tileddirectional backlight including a grating coupler. Further, FIG. 48Ashows a further embodiment for arranging stepped waveguides in an arrayincluding a grating coupling element 260. The directional backlights ofFIGS. 48A and 48B may include at least a stepped waveguide 1 and a lightemitting element illuminator array 15. Light emitting elementilluminator array 15 may be arranged on the rear side 8 of the steppedwaveguide 1 at the thin end of the stepped waveguide 1. Incident lightrays 264 may be incident on the element 260 and may be reflected intothe input aperture of the stepped waveguide to be guided within thestepped waveguide. Element 260 may include, for example, a surfacerelief diffractive reflector or a volume reflection hologram includingstacks of holograms to optimize efficiency. Light ray 262 is reflectedby end 4 of waveguide 1 so that a small seam is achieved betweenadjacent waveguides and light may be guided by features 10 and reflectedby features 12 in proximity to an adjacent waveguide 1.

In one embodiment one or more of the directional backlights may includean input end that is an extension of one of the guide surfaces, and acoupler facing the input end and arranged to substantially deflect inputlight along the waveguide.

FIG. 48B is a schematic diagram illustrating in side view, a directionalbacklight including a grating coupler. FIG. 48B shows a similarembodiment to FIG. 48A in which the coupling region including element260 may be arranged behind the side 4 of a stepped waveguide 1. Lightrays 266, 268 from light extraction features 12 may be arranged to bedirected substantially away from the side 4 of the upper steppedwaveguide, to avoid interaction with the side 4 which may include amirror surface. Diffuser 68 may be arranged to blur light in thisregion. In one embodiment one or more of the directional backlights mayinclude an input end that is an extension of one of the guide surfaces,and a coupler facing the input end and arranged to substantially deflectinput light along the waveguide.

FIG. 49 is a schematic diagram illustrating in side view, a directionalbacklight including a prismatic coupler. The directional backlights ofFIG. 49 may include a stepped waveguide and a light source illuminatorarray 15. Further, FIG. 49 shows a further embodiment including an arrayof inclined elongate surfaces 270, 272 arranged to substantially directlight from illuminator array 15 into the stepped waveguide of thestepped waveguide 1. Thus light rays 280 may be incident on surface 270and substantially reflected into the stepped waveguide 1. Light rays 284incident on surface 272 may be reflected in the opposite direction andmay be incident on surface 274 and may be reflected into the steppedwaveguide 1. Absorbing elements 276 may be arranged to capture lightfrom non-guiding modes of propagation in the stepped waveguide.

In one embodiment one or more of the directional backlights may includean input end that is an extension of one of the guide surfaces, and acoupler facing the input end and arranged to substantially deflect inputlight along the waveguide.

Advantageously the present embodiments may achieve coupling of lightfrom a light source array that is positioned to the rear of the steppedwaveguide. This may provide a more compact arrangement for tiling andstacking implementations. Further, the gap between stepped waveguidesmay be reduced.

FIG. 50 is a schematic diagram illustrating in front view, thearrangement of the viewing zones from an autostereoscopic directionaldisplay device including a single illumination region with an observerat the window plane. Further, FIG. 50 illustrates the diamond shapedviewing regions 1152 and 1150 corresponding to viewing windows 1114,1116 at the window plane 1106 for a given size of display 1100. At theplane 1156, the useful viewing regions 1152, 1150 may provide only asingle lateral viewing location without observer tracking Forward of theline 1156, an autostereoscopic image may not be seen across the whole ofthe display. Thus, as shown in FIG. 50, the forward range 1196 for 3Dviewing may be from the window plane towards the display 100 with asingle valve optical element.

In one embodiment, an autostereoscopic display apparatus including thedisplay device may further include a control system which may bearranged to selectively operate the light sources to direct light intoviewing windows corresponding to output directions. The control systemmay be arranged to control the display device to display temporallymultiplexed left and right images and substantially synchronously todirect the displayed images into viewing windows in positions which maycorrespond to the left and right eyes of an observer.

Further, the control system may include a sensor system which may bearranged to detect the position of an observer relative to the displaydevice. The control system may be arranged to direct the displayedimages into viewing windows in positions corresponding to left and righteyes of an observer, which may depend on the detected position of theobserver. Additionally, the sensor system may be arranged to detect theposition of an observer relative to the display device laterally andlongitudinally to the approximate normal to the spatial light modulator.The control system is arranged to direct the displayed images intoviewing windows in positions corresponding to left and right eyes of anobserver, in dependence on the detected position of the observer.

FIG. 51 is a schematic diagram illustrating in front view, thearrangement of the near viewing zones from an autostereoscopicdirectional display device including multiple illumination regions withan observer at the window plane. Further, FIG. 51 shows that theillumination system behind the spatial light modulator 1206 may beprovided by an array of optical valves 1200, 1202, 1204. By way ofillustration, only the portion of the viewing diamonds between thewindow plane and display 1100 are shown, although the followingdiscussion may be applied to the region behind the window plane. Eachoptical valve 1200, 1202, 1204 may illuminate a respective left eyeviewing window 1218, 1220, 1222, and may provide forward viewing zones1208, 1210, 1212. At the window plane, the viewing windows 1218, 1220,1222 may be overlapped and the observer can see a left eye image acrossapproximately the whole of the display 1100 area.

Advantageously the present embodiments increase the longitudinal viewingfreedom for displays by reducing the size of the individual opticalvalves. Such an embodiment may be advantageous for large area displays,such as televisions and monitors when viewed from short distances aswell as for mobile displays with an extended range of viewing freedom.

FIG. 52 is a schematic diagram illustrating in front view, thearrangement of the near viewing zones from an autostereoscopicdirectional display device including multiple illumination regions withan observer between the window plane and the display. Further, FIG. 52shows that in combination with an observer tracking system, thelongitudinal viewing freedom can be further extended. Observer 99 movingin direction 1221 may be tracked so that respective optical valves mayproduce viewing windows 1218, 1220, 1222 that may no longer beoverlapping in the window plane 1106. Thus the optical valves andrespective approximately aligned light emitting element arrays maycooperate to direct light to an observer such that the illumination ofthe plurality of aligned light emitting element arrays may beindependently controlled to provide illumination in alignment with thethree dimensional location of the observer. In this manner, an observercan be advantageously tracked over a wide longitudinal viewing range1216.

FIG. 53 is a schematic diagram illustrating in front view, thearrangement of the near viewing regions from an autostereoscopicdirectional display device including multiple illumination regions for amoving observer between the window plane and the display. Further, FIG.53 shows the embodiment of FIG. 52 when the forward positioned observer99 has translated in direction 1226. Thus it can be seen that bytranslating separate viewing windows 1218, 1220, 1222, the observer canmaintain an autostereoscopic image across the display surface over awide range of lateral and longitudinal viewing positions. Longitudinaltracking may be achieved by adjusting viewing window 1218, 1220, 1222separation for each of the respective optical valves and lateraltracking may be achieved by adjusting position of the set of viewingwindows 1218, 1220, 1222 by means of controlling illumination ofrespective optical windows.

FIG. 54 is a schematic diagram illustrating a limit of longitudinalviewing freedom for an autostereoscopic directional display deviceincluding multiple illumination regions. Further, FIG. 54 shows thelimit of viewing freedom in a three segment optical valve display can beincreased by increasing the size of the respective viewing windows 1219,1221, 1223 compared to the viewing windows of FIG. 53. Two or moresegment optical valves may be used. However, for very wide angle devicesit may be desirable to provide even closer viewing. This may be achievedusing the apparatus of FIG. 55 or FIG. 56 for example as will bedescribed below.

By way of comparison with known spatially multiplexed longitudinaltracking displays, an observer may be tracked without adjusting the SLMto show mixed slices of left and right views in a single illuminationphase, thus higher display resolution may be advantageously achieved.

In the above stacked embodiments, the transmission of light from thelower element may be lower than for the upper element. The outputluminance of the light emitting elements may be adjusted to compensatefor this difference.

FIG. 55 is a schematic diagram illustrating a front view of a waveguideincluding first and second light reflecting sides for a firstillumination arrangement. Optical valve 900 includes first curved side902 and second curved side 904 arranged to achieve a tiled optical valveas described above. Light source arrays 906, 908 are arranged toilluminate respective sides 902, 904 so that source 907 and source 909are illuminated for a given optical window of the viewing window 26. Ifan air gap is provided between the light source arrays 906, 908, and theinput side 901 to the tiled optical valve, then typically Lambertianillumination profile will be provided in air, that is coupled byrefraction into a profile with a cone angle of +/−θ_(c) where θ_(c) isthe critical angle of the material of the optical valve. Thus polarintensity distributions 910, 912 are produced inside the valve. It wouldbe desirable to reduce the visibility of the seam 916 between the firstand second curved sides 902, 904. In operation, light rays 918, 922 aredirected towards the seam 916 so that rays 914 propagate parallel to theseam 916 after reflection at sides 902, 904. From the polardistributions 910, 912 it can be seen that the intensity of the rays 914will be different either side of the seam 916, illustrated by therelative separation 926 of the lines 920, 924 with respect to the twodistributions 910, 912. Further, the distance of the source to the cusp905 may be different for the two sources 907, 909, thus furtherproviding a difference in intensity of rays 914 either side of the seam916. Undesirably this may provide an illumination discontinuity at thedisplay surface.

FIG. 56 is a schematic diagram illustrating a front view of a waveguideincluding first and second light reflecting sides for a secondillumination arrangement. Sources 930, 932 are provided at a greaterdistance from the centre of the arrays 906, 908 and thus the separation934 is increased, thus providing a greater intensity difference acrossthe seam 916 for rays 914.

FIG. 57 is a schematic diagram illustrating graphs of display luminanceacross the width of the optical valve for various illuminationarrangements for a horizontal cross section A-A′ across the opticalvalves of FIGS. 55 and 56. For on-axis sources, distribution 944 may beachieved. At the cusp region, the intensity variation may changedirection, but there is no discontinuity in the intensity distribution.If further diffusers are added, such a difference may have lowvisibility. Distribution 946 may be provided by light source arrangementof FIG. 55 and distribution 948 by the arrangement of FIG. 56. Thus adiscontinuity 950 in intensity at the seam 916 may be provided.

FIG. 58 is a schematic diagram illustrating a front view of a waveguideincluding first and second light reflecting sides for a thirdillumination arrangement. A control system (not shown) may be providedto modulate the greyscale output of the respective light sources 930,932. Thus the distribution 912 may be reduced in intensity compared tothe distribution 910 so that the intensity of the rays 914 aresubstantially matched either side of the seam 916.

FIG. 59 is a schematic diagram illustrating graphs of display luminanceacross the width of the waveguide for various illumination arrangements.Thus the display illuminance distribution 944 may be achieved by thearrangement of FIG. 58. Further, addition of a diffuser with somediffusion in the lateral direction may achieve the distribution 952.Advantageously the uniformity of illumination of the display isincreased and the appearance of the seam 916 is minimized.

FIG. 57 is a schematic diagram illustrating graphs of display luminanceacross the width of the optical valve for various illuminationarrangements. Distribution 944 may be provided by the correctedintensity of the respective light sources 930, 932 and after a diffusoris provided between the valve and observer, distribution 944 may beachieved. Advantageously the uniformity of the display output across itsarea may be increased. Such an arrangement can achieve desirableuniformity performance for tiled valves, increasing display area andreducing display bezel size as well as reducing display aberrations.

Advantageously, the diffractive reflector 800 may be tuned to the peakemission wavelengths of the light emitting elements of the array 15 asshown in FIG. 60 including respective layers 802, 804, 806 oralternatively recorded within a single layer, corresponding to peakemission of red light emitting element 808, green light emitting element810 and blue light emitting element 812. The reflector 800 may includestacks of red, green and blue reflection diffractive elements or may beformed by multiple recordings in a single layer. Thus the reflected rays815, 816, 817 are collimated across a broad spectral band from a flatelement. Advantageously, such an arrangement achieves a non-metalizedreflector that is planar. Advantageously, such an arrangement may reducestray light by way of comparison with poorly finished plastic surfacesthat are metalized. Thus such an arrangement may have reduced crosstalk.

FIG. 61 shows that further layers or diffractive reflective structuresmay be incorporated into the reflector 800 to achieve higher qualityoff-axis imaging so that advantageously, the viewing angle of thedisplay may be increased compared to spherical surface mirrors. Thus,the layers 803, 805, 807 may be optimized for separated light emittingelement 808, 810, 812, providing collimated output rays 818, 819, 821for guiding within the optical valve 1.

The light emitting elements may include narrow band emission to providehigh efficiency of reflection. The reflector 800 may be recorded toprovide low aberrations and high efficiency over a range of illuminationangles including the length of the array 15, and may include multiplediffractive structures to achieve high efficiency over the respectiverange of illumination angles.

The reflector 800 may further incorporate a diffusing function that isdifferent in x and y directions, so as to achieve limited blurringacross the windows (y axis) while larger blurring in the verticaldirection (x-axis). Advantageously, the asymmetric diffusers may beremoved, reducing cost and complexity.

FIG. 62 shows a method to form the diffractive mirror 800 on a waveguide1. Side 4 may be expensive to provide with an accurately polished andreflective surface on a plastic optical valve 1. The reflector 800 maybe provided by a roller 892 rolling in direction 894 onto the top side 4and an index matching adhesive 898 to provide an optically transparentinterface to the reflector 800.

FIG. 63 shows a further embodiment to control stray light losses inoptical valves, illustrating the top view of side 4. Chips or othererrors in the corners of the side 4 in contact with side 6 and feature10 may create unwanted non-uniformities in light output. Advantageously,an absorbing region 895 and mirror region 897 may be provided on theside 4 to reduce non-uniformities and reduce stray light. The region 895may be formed by printing for example, either directly onto the side 4prior to forming the reflector 800 on the side 4.

As may be used herein, the terms “substantially” and “approximately”provide an industry-accepted tolerance for its corresponding term and/orrelativity between items. Such an industry-accepted tolerance rangesfrom approximately zero percent to ten percent and corresponds to, butis not limited to, component values, angles, et cetera. Such relativitybetween items ranges between approximately zero percent to ten percent.

While various embodiments in accordance with the principles disclosedherein have been described above, it should be understood that they havebeen presented by way of example only, and not limitation. Thus, thebreadth and scope of this disclosure should not be limited by any of theabove-described exemplary embodiments, but should be defined only inaccordance with any claims and their equivalents issuing from thisdisclosure. Furthermore, the above advantages and features are providedin described embodiments, but shall not limit the application of suchissued claims to processes and structures accomplishing any or all ofthe above advantages.

Additionally, the section headings herein are provided for consistencywith the suggestions under 37 CFR 1.77 or otherwise to provideorganizational cues. These headings shall not limit or characterize theembodiment(s) set out in any claims that may issue from this disclosure.Specifically and by way of example, although the headings refer to a“Technical Field,” the claims should not be limited by the languagechosen under this heading to describe the so-called field. Further, adescription of a technology in the “Background” is not to be construedas an admission that certain technology is prior art to anyembodiment(s) in this disclosure. Neither is the “Summary” to beconsidered as a characterization of the embodiment(s) set forth inissued claims. Furthermore, any reference in this disclosure to“invention” in the singular should not be used to argue that there isonly a single point of novelty in this disclosure. Multiple embodimentsmay be set forth according to the limitations of the multiple claimsissuing from this disclosure, and such claims accordingly define theembodiment(s), and their equivalents, that are protected thereby. In allinstances, the scope of such claims shall be considered on their ownmerits in light of this disclosure, but should not be constrained by theheadings set forth herein.

What is claimed is:
 1. A directional display device, comprising: atransmissive spatial light modulator comprising an array of pixelsarranged to modulate light passing therethrough; and at least twodirectional backlights, each comprising: a waveguide having an inputend, first and second, opposed guide surfaces for guiding light alongthe waveguide, and a reflective end facing the input end for reflectinglight from the input light back through the waveguide, the first guidesurface being arranged to guide light by total internal reflection, thesecond guide surface comprising a plurality of light extraction featuresoriented to reflect light guided through the waveguide after reflectionfrom the reflective end in directions allowing exit through the firstguide surface as output light, the waveguide being arranged to directinput light originating from different input positions in a lateraldirection across the input end into respective optical windows in outputdirections distributed in the lateral direction in dependence on theinput positions, the directional backlights each being arranged tosupply output light through the spatial light modulator; in respect ofeach directional backlight, an array of light sources at different inputpositions across the input end of the respective waveguide; a controlsystem arranged to selectively operate the light sources to direct lightinto said optical windows corresponding to said output directions, thecontrol system further comprising a sensor system arranged to detect theposition of an observer relative to the display device, the controlsystem being further arranged to control the display device to displaytemporally multiplexed left and right images and synchronously to directthe displayed images into viewing windows in positions corresponding toleft and right eyes of an observer, in dependence on the detectedposition of the observer.
 2. A directional display device according toclaim 1, wherein the directional backlights are tiled behind the spatiallight modulator so as to supply output light through different regionsof the spatial light modulator.
 3. A directional display deviceaccording to claim 2, wherein the directional backlights are tiled in adirection perpendicular to the lateral direction.
 4. A directionaldisplay device according to claim 3, wherein the reflective end of afirst one of the directional backlights overlaps a second directionalbacklight.
 5. A directional display device according to claim 3, whereinthe directional backlights include two directional backlights havingreflective ends that are substantially coplanar.
 6. A directionaldisplay device according to claim 5, wherein said reflective ends thatare coplanar are substantially flat.
 7. A directional display deviceaccording to claim 5, wherein said reflective ends that are coplanareach comprise a diffractive reflector having positive optical power in alateral direction.
 8. A directional display device according to claim 3,wherein the directional backlights are also tiled in the lateraldirection.
 9. A directional display device according to claim 2, whereinthe directional backlights are tiled in the lateral direction.
 10. Adirectional display device according to claim 2, wherein the waveguidesof the directional backlights are formed from a common piece ofmaterial.
 11. A directional display device according to claim 1, whereinthe directional backlights are stacked behind the spatial lightmodulator and each supply output light through the spatial lightmodulator and through any other directional backlight intermediate thedirectional backlight and the spatial light modulator.
 12. A directionaldisplay device according to claim 11, wherein the directional backlightsare oriented around the normal to the spatial light modulator so thatthe optical windows provided by the directional backlights areapproximately aligned with each other.
 13. A directional display deviceaccording to claim 1, wherein the first guide surfaces of the respectivedirectional backlights are substantially coplanar.
 14. A directionaldisplay device according to claim 11, wherein the directional backlightsinclude two directional backlights that are arranged in invertedorientations around the normal to the spatial light modulator with theinput end of each directional backlight on the same side as thereflective end of the other directional backlight.
 15. A directionaldisplay device according to claim 14, wherein the facing guide surfacesof the two directional backlights that are arranged in invertedorientations extend in a generally parallel direction.
 16. A directionaldisplay device according to claim 11, wherein the directional backlightsare oriented around the normal to the spatial light modulator so thatthe optical windows provided by the directional backlights extend at anangle relative to each other in a range from 85 to 95 degrees.
 17. Adirectional display device according to claim 1, wherein the reflectiveend of each directional backlight has positive optical power in alateral direction across the waveguide.
 18. A directional display deviceaccording to claim 1, wherein the light extraction features of eachdirectional backlight have positive optical power in a lateral directionacross the waveguide.
 19. A directional display device according toclaim 1, wherein, in each directional backlight, the second guidesurface has a stepped shape comprising facets, that constitute saidlight extraction features, and intermediate regions between the facetsthat are arranged to direct light through the waveguide withoutextracting it.
 20. A directional display device according to claim 1,wherein at least one of the directional backlights comprises an inputend that is an extension of one of the guide surfaces, and a couplerfacing the input end and arranged to deflect input light along the waveguide.
 21. A directional display device according to claim 1, whereinthe at least two directional backlights are oriented around the normalto the spatial light modulator so that the optical windows provided bythe directional backlights are approximately aligned with each other andthe array of light sources in respect of each directional backlight isarranged to output light of a different colour.
 22. A directionaldisplay device according to claim 1, wherein the sensor system isarranged to detect the position of an observer relative to the displaydevice laterally and longitudinally of the normal to the spatial lightmodulator and the control system is arranged to direct the displayedimages into viewing windows in positions corresponding to left and righteyes of an observer, in dependence on the detected position of theobserver.